In recent years, anthracnose disease (black spot, black dot, black dot) caused by the fungus Colletotrichum coccodes has spread in the main areas of potato cultivation. Manufacturers and researchers have long considered it a minor disease of no significant importance. But the increase in harmfulness against the background of increased requirements for the quality of tubers both in fresh form and in the processing industry transferred anthracnose to the category of an economically important disease that causes significant economic losses. According to scientific publications (Kuznetsova M.A. et al., 2020), anthracnose on potatoes was not widespread in Russia until about the mid-1950s. Then there was a gradual increase in the disease. In 1980-1985, the defeat of potato plants by anthracnose ranged from 5 to 25%, in 1986-1987 from 10 to 35%, in the hot and dry summer of 1988, the defeat of tops was from 10 to 70%, in 1989 - from 5 to 40%, in 1990-2000 - from 3 to 35%, in 2001-2009 - from 2 to 55%, in the hot and dry summer of 2010 from 5 to 100%, in 2011-2019 - from 3 to 65 %. Researchers agree that the main reasons for the increase in the severity of anthracnose are the import of infected seed material, spread with seeds, damage to tubers during mechanized cultivation, and a decrease in plant resistance against the background of unfavorable growing conditions. Anthracnose can directly reduce the yield of potatoes by 12-30%, worsen product quality due to external spots on the skin, discoloration of internal tissues and lead to a decrease in the marketability of the crop during storage.
Anthracnose symptoms. The fungus Colletotrichum coccodes can appear on tubers, stolons, roots, stems and leaves of potatoes. On the aerial parts of plants, the first symptoms of anthracnose are manifested in yellowing and drying of the leaves. At the same time, the stems remain green for a long time (photo 1). Only by the yellowing of the leaves, anthracnose is not determined. Drying of potato leaves can be caused not only by anthracnose, sclerotinia, pectobacteria, but also by cercosporosis, alternariosis, and verticillium (wilt). As a result of the joint manifestation of new types of infections, atypically early drying of potato plants is increasingly observed in production.
In the second half of the growing season, the disease affects the stems. First, small bronze spots appear in the area of attachment of dried leaves (photo 2). Then the affected area expands (photo 3). In the future, the spots increase, a white coating of mycelium appears on them. The tissue of the stem under the mycelium changes color from bronze to black (photo 4,5). White plaque on the stems is also caused by rhizoctoniosis, sclerotinia, and gray rot.
Photo 2,3. Anthracnose development on stems
Photo 4,5. White bloom of anthracnose mycelium on stems
Anthracnose spots also affect the underground zone of the stems. In color, they are similar to the manifestation of rhizoctoniosis (photo 6). However, in rhizoctoniosis, unlike anthracnose, the border between the affected and healthy tissue is very clear.
With the further development of anthracnose on the underground part of the plant at the site of damage to the stems, stolons, roots, the surface rots, exfoliates and is easily separated (photo 7). In high humidity, the damage takes on a light purple hue.
Damaged stems are easily pulled out of the ground. Many black microsclerotia are formed at the site of infection of the stems (photo 8). Hence the English name of the disease - black dot (black dot). But this is also not an exceptional symptom; sclerotia also form verticillium and white rot.
The symptoms of anthracnose on tubers vary considerably. Initially, these are gray disordered spots on the peel. During storage, a silvery tint appears (photo 9). In contrast to the silver scab, the anthracnose spots are less sharply separated from the healthy peel and microsclerotia are visible on the spots (photo 10). Typical black spotting with silvery brown spots appears on the surface of the tuber with saturation throughout the diseased tissue of small black microsclerotia. Severely affected tubers shrivel, the skin is easily peeled off from the surface, where small sclerotia are also formed. The surface of the tubers is uneven, bumpy. On the cut of the affected tubers, a brown-colored tissue can be traced to a depth of 0.5-0.8 cm, with time hard depressed spots appear. With prolonged incubation in storage conditions, the symptoms of the disease spread throughout the tuber, weeping tissue appears, mucus and complete destruction of such tubers.
Photo 9. Symptoms and sclerotia of anthracnose on tubers
With a strong development of anthracnose, depressed spots, peel ruptures, dark damage to the vascular ring and tuber pulp are noted, which are somewhat different from other tuber diseases (phytophthora, phomosis, fusarium, ditylenchosis), but not unambiguously. Visual symptoms and at this stage are not enough to identify the pathogen (photo 11).
Sources of infection and factors in the development of anthracnose. Infection of potatoes with C. coccodes can be caused by soil, tuber and airborne inoculum. Soil inoculum, as a rule, has a greater harmfulness compared to tuber. In the soil, the fungus can exist either as sclerotia or as conidia at undetectable levels. Previously, it was believed that sclerotia survive in the soil for more than 4 years, currently there are claims to increase this period to 8-15 years. The pathogen overwinters in the form of sclerotia on the surface of affected tubers, on plant debris and in the soil. In spring, spores are formed on plant debris, tubers and spread with moisture drops in the soil and on the plant. During the summer, spores germinate in drip-liquid moisture and are able to infect all parts of the plant. Reinfection of plants occurs many times per season, spores are spread by wind, insects, raindrops. C. coccodes often infects potato stems and other tissues early in the growing season, but symptoms of chlorosis and leaf necrosis, as well as sclerotia signs of the pathogen, often do not appear until relatively late in the growing season.
Infected seed tubers are usually the initial source of soil infection and an important source of infection for roots, stolons and daughter tubers. Any part of the surface of the tuber can be infected with C. coccodes and this can lead to subsequent infection of the stem. It is not possible to detect all infestation in a batch because the fungus may occupy a small part of the surface or be located inside the tuber. Seeds without visible signs of C. coccodes may be infected. The fungus from the seed material gradually colonizes the soil, moving away from the infected tuber at a rate of 1 mm per day. Infection of the maternal seed has a permanent effect on the infection of the progeny, and this infection from the maternal seed begins shortly after planting. Seed tubers with external infection produce progeny tubers with the highest frequency and severity of infection, as well as stem infection and the number of tubers affected at the end of the stolon. Similar levels of the disease develop on tubers and stems of plants grown from healthy tubers but near seed tubers with internal or external infection. Anthracnose mycelium moves in the soil from infected seed tubers to daughter tubers of neighboring plants. There is no correlation between tuber surface infection and internal infection. However, all tubers with internal infections also had external infections. Vascular infection of C. coccodes in seed tubers is of particular concern because vascular infections are unlikely to be controlled by treating infected tubers with fungicides applied to the tuber surface.
What is the cause of the defeat - infected seed material, contaminated soil, airborne transmission? This can be found out by some features of the lesion. The airborne lesion is similar in appearance to alternariosis, but concentric rings do not form within the lesion. In regions prone to dust storms, there is a high risk of leaf infestation in this manner, as sand wounds provide pathways for the fungus to enter. The high frequency of infection of tubers at the stolon end indicates that the primary infection of daughter tubers occurred due to the penetration of the pathogen through the stolons, i.e. from the mother tuber. In one study, a field was planted with apparently clean seeds in new soil, but 15 to 88% of the daughter tubers were found to be infested.
If the soil is the main source, then the development of microsclerotia on tubers occurs randomly over the entire surface of the tubers. Symptoms of black spot appear at a high frequency in root tissue (60 to 90%) at the date of first assessment 5 weeks after planting, regardless of the level of inoculum (low or high), but on stems that are underground, the disease is visible at this time little or no at all. A similar study on tuber-borne inoculum showed that symptoms on roots and stolons can be detected around the time of emergence, while symptoms on stems appear about 7-10 weeks after inoculation. Studies conducted under commercial growing conditions in the state of Washington (USA) showed that C. coccodes appears as early as 15 days after emergence on aboveground stems, and later, 22 days after emergence on underground stems; however, more infection was usually isolated from underground stems on subsequent sampling dates.
Under field test conditions in Scotland, C. coccodes colonization of root tissue obtained from disease-free micropropagated plants was similar to that in roots obtained from both visually clean and defective seed tubers when assessed at the beginning of the growing season, but was significantly lower at later sampling dates. In the Idaho trials, colonization of stem tissue by C. coccodes above and below ground was higher than the frequency of colonization of stolons and roots. This trend continued regardless of whether the infection was due to contamination of the soil, seed tubers, or foliar inoculation. This is in contrast to previous studies which have demonstrated that symptoms of black spot disease can be found first in root tissue compared to other plant tissues evaluated. Different studies assessed different indicators: the severity of symptoms or the colonization of tissues by the fungus, which is the most likely reason for the discrepancies. It is generally accepted that C. coccodes infections remain latent for longer periods of time in stems compared to roots and stolons.
Studies comparing the effects of soil and seed have shown that soil infection causes more black spots than seed-borne infection. In the field in England, varying levels of seed tuber inoculum resulted in an increase in anthracnose infection at stem bases and roots, but not proportional to the level of seed tuber infection, while the level of soil infection functionally determines the level of anthracnose infection. Increasing the amount of soil inoculum increases the severity of the disease, including leaf necrosis and chlorosis, as well as the development of scleroses on roots and stems.
Knowing how fields are contaminated with black dot inoculum helps make decisions about site selection, the use of fungicidal tillage, or which variety to grow in a particular field. For anthracnose, an accurate testing methodology based on DNA PCR analysis has been developed and the relationship between the level of inoculum in the soil and the risk of potato disease has been established. The soil sampling procedure for the anthracnose test is similar to the nematode test. Anthracnose target DNA is quantified by PCR and is expressed as pg DNA/g of soil (pg is a picogram or trillionth of a gram). Soil test results categorize risk as low (0-100 pg DNA/g soil), medium (101-1000 pg DNA/g soil), and high (>1000 pg DNA/g soil) based on the impact of soil contamination on potatoes. If the threshold is low, then there is little risk of disease-causing levels of anthracnose that could affect marketability. If the threshold is high, there is a high risk that the marketability of a significant proportion of the tubers will be reduced unless mitigation measures are taken (Figure 13). However, the patterns of development of anthracnose in many studies turned out to be very contradictory, and infection of the soil or seed material does not always cause a corresponding decrease in the yield and quality of tubers. The fact is that the consequences of infection with anthracnose, ultimately, always depend on a unique combination of external conditions and agrotechnical features in production conditions.
The optimal temperature for the growth of C. coccodes hyphae is 24 оC. The formation of sclerotia and subsequent infection of plant tissue occurs over a wide range of temperatures. No symptoms were observed on tubers at 15 оC, but at this temperature a large number of infected stems were found. Aeration and light also influence the germination of sclerotia. Conidia are formed in greater numbers on above-ground sclerotia.
Anthracnose is most commonly associated with light sandy soils, high temperatures, and poor water drainage. However, the diversity of damage in plants exposed to stress makes it difficult to identify trends in the influence of abiotic and biotic factors on the development of the disease. In the US, excessive rainfall, irrigation, and low temperatures early in the season, followed by a prolonged drought, have led to the spread of the disease. In England, irrigation reduced infection of stems, roots and tubers up to 18 weeks after planting, but increased in later stages. In Israel, where all crops are regularly irrigated, disease and crop losses have been observed at high temperatures and relatively dry soil.
All potato varieties are susceptible to C. coccodes, but to varying degrees. Foreign studies have shown that thin-skinned varieties are more susceptible to anthracnose than thick-skinned varieties. There are significant differences between varieties in the frequency of colonization of the stems and the severity of damage to the surface of the tubers. Differences between stem and tuber infection have been observed in some cultivars, for example Desiree has the lowest stem infection but one of the highest tuber infection rates. The severity of infection is higher in early varieties because the tubers are in contact with the soil inoculum for a longer period. Variations occur in both early and late varieties, suggesting a genetic influence. In the Russian Federation, separate studies of the resistance of potato varieties to anthracnose have been carried out. For example, the VIZR monitoring of tuber material of elite categories in the North-West region showed that the varieties least affected by anthracnose were Gala, Lomonosovsky, Eurasia, Labadiya and Sudarynya, and the most susceptible were Nevsky, Red Scarlett, Charodey and Aluet.
The frequency of occurrence of anthracnose on tubers is higher with one-three-year potato crop rotations. The incidence of anthracnose decreases significantly as the number of years between potato crops increases. C. coccodes is found in fields without potatoes for 10 and 15 years, but infection rates become low after 6 or more years without potato production. Many species of cultivated and weed plants are affected by anthracnose, are host plants and contribute to the long-term persistence of the infection in the soil. Foreign studies have shown that it has a wide range of hosts, which includes at least 58 species and 17 families, primarily vegetables from the nightshade family - tomato, eggplant, red pepper, tobacco. But carrots, onions, broccoli, lettuce, table and sugar beets, rape, yellow mustard are also affected. Wheat, corn, soybeans, sunflower, cereal grasses, beans, peas are not susceptible to the disease. Decay products released by some plant species - cruciferous, sweet clover, lupine, sorghum-sudanese hybrid reduce the growth of many types of pathogenic fungi. Sideration of biofumigant crops reduces the severity of anthracnose.
Many weeds (black nightshade, field bindweed, white gauze, shepherd's purse, common nettle, knotweed, European heliotrope, etc.) can lead to an increase in the amount of inoculum or can serve as a source of primary inoculum for potatoes. The inoculum of C. coccodes survives in the soil not only on other host species, but also on potato tubers left in the field after harvest. They germinate the next year and accumulate many diseases. Weed potato tubers remain viable for several years after the initial harvest. Volunteer control, i.e. voluntary potato is critical to reduce the amount of primary anthracnose inoculum in the soil.
Plant stress caused by nutrient deficiencies or imbalances can also increase anthracnose colonization of potato roots. In controlled experiments, nitrogen was given at 5, 40, 160, and 640 ppm to stress plants from nitrogen deficiency and excess. Rooted plants were inoculated with a suspension of C. coccodes spores. Root system colonization was greatest at the lowest nitrogen level (5 ppm). Root colonization decreased as nitrogen concentration increased to 160 ppm, which was the optimal N level, and then increased as nitrogen increased to 640 ppm. When testing for potassium, the greatest root colonization occurred at the lowest level of potassium (0 mg K) and decreased as the concentration of potassium was increased to 80 mg (optimal K), and then slightly increased as the concentration of potassium was increased to 160 mg K. The same pattern observed when testing phosphorus. The greatest root colonization occurred at the lowest level of phosphorus (0,032 ml), and then decreased as the concentration of phosphorus increased to the optimal level of P (1,00 ml). Thus, potato roots are more heavily colonized by black dot fungus when plants are under stress from both deficiency and excess of nitrogen, potassium, and phosphorus than when optimal levels of each nutrient are available to plants.
Irrigation of potatoes after the tops have dried increases the frequency and severity of anthracnose damage to tubers by at least two times. The severity of tuber infection and the number of tubers affected at the stolon end were significantly higher in tubers grown from top-watered plants compared to bottom-watered ones. Water moving down the soil plays a significant role in moving the inoculum from the infected tuber seed to the daughter tubers.
Studies have also shown that the frequency and severity of anthracnose increases on unwashed tubers when stored at 15 оC versus 5 оC and that early harvest and storage of tubers dry can prevent or reduce the onset of the disease. The development of black spots on tubers is minimized by immediately chilling the crop compared to tubers kept at 12°C for 10 days before chilling. However, it is important to properly dry the crop to avoid the development of rot. In long-term storage, there is no difference between the appearance of the disease on tubers kept at 2,5°C or 3,5°C.
Potato anthracnose management options consist in the use of preventive measures and protection with the help of fungicides. One of the most important principles of black spot control is to reduce the amount of inoculum in the soil due to the effect of crop rotation, removal of crop residues, weed potatoes and weeds. Even the longest crop rotation with non-host crops (for example, cereals, soybeans or corn) does not completely heal the soil (since anthracnose microsclerotia persist in the field up to 8-15 years), but reduces the level of inoculum several times.
To prevent and reduce the incidence of this disease, the following measures should be taken:
1. Selection of varieties with high resistance to anthracnose, avoiding the cultivation of susceptible varieties on infected fields;
2. Use certified seeds from reputable manufacturers and test them in the field or store before purchasing. Avoid infected seeds of more susceptible varieties. The regulations for the certification of seed potatoes of all countries currently do not provide for the regulation of anthracnose, since there is no direct connection between the defeat of the uterine tuber and the development of infection on daughter tubers. PCR studies of samples with symptoms of anthracnose on leaves conducted in the Russian Federation showed that out of 96 samples, only 5 were affected by anthracnose. At the same time, in the US and UK, the incidence of C. coccodes in certified seed tubers varies from 0 to 90% and 0-75%, respectively. Infected imported seeds are the main channel for the spread of anthracnose to the potato growing regions of the Russian Federation;
3. Test seed for C. coccodes to determine if fungicide treatment is needed. Do not plant infected seeds in clean, anthracnose-free fields;
4. Avoid planting potatoes in poorly drained soil;
5. Carrying out moldboard basic tillage ensures deep incorporation of plant residues and their decomposition;
6. Balanced and sufficient fertilization;
7. Avoid over-watering, especially in susceptible and late maturing varieties. Reducing the amount of water between desiccation and harvest
8. Harvesting of tubers as soon as possible after desiccation of haulm;
9. Rapid cooling of potatoes in storage. Precise temperature and humidity control during storage. High temperatures and condensation on the surface of the tuber contribute to the disease;
10. Soil biofumigation with green manure of white mustard, oil radish, sweet clover, sorghum-Sudanka hybrid.
If anthracnose infection is found on the tubers and in the soil, specialized fungicides should be applied.
Chemical protection against anthracnose. For a long time, fungicides with azoxysrobin were the only means of controlling soil infection. In numerous tests, azoxystrobin, applied by furrow application at planting or incorporation into the soil, shows a consistent reduction in anthracnose. This treatment delays the development of the disease for several weeks. Since azoxystrobin belongs to strobirulins (FRAC class 11) capable of inducing resistance, i. resistance of pathogens in it, then this topic is actively discussed, especially by competing manufacturers of plant protection products.
Currently, the list of active molecules used against anthracnose has been significantly expanded, since it turned out that infection of potatoes occurs throughout the growing season. Azoxystrobin remains the benchmark for effectiveness against anthracnose, but should not be used more than once per season. The widest list of fungicides against anthracnose is registered in the USA (Table 14). Several preparations are recommended for introduction into the furrow during planting, the rest - during the growing season of potatoes.
Table 14. List of fungicides for the control of potato anthracnose, USA, 2021
black dot | azoxystrobin | 6.0 – 15.5 fl oz Aframe, Equation, Quadris Flowable, Satori, Willowood Azoxy 2SC | 14 |
Do not exceed one application of a Group 11 fungicide before alternating with a fungicide containing a different mode of action Quadris and Headline are Group 11 fungicides.
Quadris Opti is a Group 11 and Group M fungicide. |
|
azoxystrobin + chlorothalonil | 1.6pt Quadris Opti | 14 | |||
azoxystrobin + difenoconazole | 8.0 – 14.0 fl oz Quadris Top | 14 | |||
pyraclostrobin | 6.0 – 9.0 fl oz Headline SC, EC | 3 | |||
azoxystrobin + benzovindiflupyr | 0.34 – 0.5 oz Elatus/1,000 ft row | 14 | Apply in-furrow at planting in a narrow band over the seed piece. Do not exceed 9.5 oz/a as a banded application. | ||
chlorothalonil | 1.0 – 1.5 pt Bravo Weather Stik Echo 720 1.5 – 2.25 pt Bravo Zn, Equus 500 Zn 0.875 – 1.25 lb Echo 90DF, Echo Zn 0.9 – 1.36 lb Bravo Ultrex 82.5WDG, Equus DF |
7 7 7 7
|
Note seasonal use limitations on the label. Current labeling for annual use of chlorothalonil products in Wisconsin allows 11.2 lb ai/a Bravo products (Ultrex, WeatherStik, Zn) (special W! registration expires 12/31/17, however a renewal is in process – please check DATCP special registration listings ) and 16.0 lb ai/a Echo products (Zn, 720, 90DF) (special WI registration expires 12/31/20). | ||
chlorothalonil + cymoxanil | 2.0pt Ariston | 14 | Apply at 7- to 14-day intervals. Use shorter interval when plants are rapidly growing and disease conditions are severe. | ||
cymoxanil + famoxadone | 6.0 – 8.0oz Tanos | 14 | Manages several other diseases. Follow resistance management guidelines. For suppression. | ||
difenoconazole | 5.5 – 7.0 fl oz Top MP | 14 | Follow resistance management guidelines. | ||
Black Dot (cont.) | fenamidone | 5.5 – 8.2 fl oz Reason | 14 | Manages several other diseases. Follow resistance management guidelines. For suppression. | |
fluopyram + pyrimethanil | 11.2 fl oz Luna Tranquility (suppression) | 7 | Begin fungicide applications preventatively. Do not apply more than 43.6 fl oz/a per season. Do not make more than 2 sequential applications of any Group 7 or 9 fungicide before rotating with a fungicide from a different group. | ||
fluoxastrobin | 0.16 – 0.24 fl oz/1,000 ft row Aftershock, Evito 480 SC 6.1 – 9.2 oz/a Tepera | 7 | Follow resistance management guidelines. | ||
flutolanil | 0.71 – 1.1lb Moncut 70-DF | at-planting treatment | Direct spray uniformly around or over seed piece in a 4- to 8-inch band prior to covering with soil. | ||
fluxapyroxad + pyraclostrobin | 4.0 – 8.0 fl oz Priaxor | 7 | Make no more than 3 applications/a per season. Apply no more than 24.0 fl oz/a per season. | ||
mancozeb | 0.4 – 1.6 qt Dithane F45 4F 0.5 – 2.0 lb Dithane M45, Penncozeb 80WP, Penncozeb 75DF 1.0 – 2.0 lb Dithane 75DF Rainshield NT, Koverall, Manzate 200 75DF |
3
3
3 |
Do not exceed a total of 11.2 lb ai/a EBDC per growing season. EBDC materials include maneb, mancozeb, and metiram. | ||
mefentrifluconazole | 3.0 – 5.0 fl oz Provysol | 7 | Do not apply more than 5.0 fl oz (0.13lb) / per acre per application. Do not male more than applications at 5.0 fl oz or | ||
Black Dot (cont.) | 5 applications at 3.0 fl oz per acre per year. | ||||
metaconazole | 2.5 – 4.0 oz Quash | 1 | Do not make more than 4 applications per season. Do not male more than 2 consecutive applications. Do not apply more than 16.0 oz/a per season. | ||
penthiopyrad | 10.0 – 24.0 fl oz Vertisan | 7 | Do not exceed 72.0 fl oz/a per year. Make no more than 2 sequential applications of Vertisan before switching to a fungicide with a different mode of action. | ||
pydiflumetofen + fludioxonil | 9.2 – 11.4 fl oz Miravis Prime | 14 | Suppression of black dot only. Do not apply more than 2 applications per year by air. Do not apply more than 34.2 fl oz per acre per year. | ||
pyraclostrobin + metiram | 2.0 – 2.9 lb Cabrio Plus | 3 | Do not male more than 2 sequential applications before alternating to a non-Group 11 or M3 fungicide. | ||
zoxamide + chlorothalonil | 32.0 – 34.0 fl oz Zing | 7 | Do not make more than 2 sequential applications before alternating to another mode of action. |
As of 2023, the active ingredients pentachloronyltrobenzin, mandipropamide + difeconazole, azoxystrobin + mancozeb, mefentrifluconazole + pyraclostrobin are also allowed in the United States. Most of the listed drugs and combinations of active molecules are allowed to be used in the Russian Federation against late blight and Alternaria.
Radical destruction of anthracnose with the help of fungicidal protection is not achieved. This is due to the extended cycle of disease development and infection from various sources: through seeds, soil and airborne droplets. The decrease in the level of development of the disease is nevertheless significant - two times (Table 15). The yield of potatoes on a high agricultural background in the best protection options (leaf processing in addition to soil application) increases by 11-14 t/ha.
Table 15. Influence of soil and foliar application of fungicides on the development of anthracnose, cultivar Russet Burbank, 2012
Signature Treatment Flagship Store IF=infurrow F=foliar @20cm | Product / ha | Visual % black dot- lower 10cm of stem | C. coccodes ng DNA/g potato stem | Yield MT/ha |
Quadris IF | 639ml | 48.2 ab | 1798.4 ab | 58.68 ab |
Quadris IF Mancozeb F | 639 ml 2.2 kg | 41.0 b | 900.7 cd | 62.52 to |
Quadris IF Priaxor F | 639ml 426ml | 31.7 c | 622.1 d | 54.36 bc |
Priaxor IF | 480ml | 50.0 to | 1542.6 ab | 54.72 bc |
Priaxor IF Bravo ZN F | 480ml 1135ml | 35.8 bc | 892.6 cd | 54.60 bc |
Priaxor IF Quadris F | 480ml 639ml | 25.6 cd | 1332.0 ab | 60.00 ab |
Priaxor IF Headline F | 480ml 426ml | 28.3 cd | 789.0 cd | 65.76 to |
Quadris IF Fontelis F | 639 ml 1.1 kg | 22.7 d | 595.1 d | 56.04 bc |
Vertisan IF Quadris F | 1646ml 639 | 35.5 | 2249 to | 57.36 bc |
Untreated | 51.5 to | 2072.9 to | 51.96 c |
The data obtained (see table 15) clearly show that one application to the soil when planting strobirulin fungicides is not enough to control this disease. In Canada, this option is even considered unreasonable; anthracnose fungicides based on azoxystrobin, difeconazole, mefentrfluconazole, benzovindiflupyr and fluopyram + pyrimethanil are recommended to be applied there only during the growing season. In fact, the effectiveness against anthracnose must be taken into account when forming a system for protecting potatoes from major diseases (alternaria, late blight) during the growing season. It was also established that the introduction of azoxystrobin at the very end of the growing season, a week after desiccation, gives an additional significant effect of reducing tuber damage.
Protection of planting material from anthracnose is currently recognized as ineffective, although many active substances (difeconazole, pyraclostrobin, imidazole) almost completely destroy the inoculum on the surface of tubers (diagram 16). But this is a short-term effect, its consequences are leveled out quite quickly, within a month, because the infection is also inside the tubers.
Finally. The harmfulness of anthracnose has recently increased significantly, this pathogen has moved into the category of economically significant problems. The fungus Colletotrichum coccodes, which causes anthracnose on potatoes, is a difficult to predict and elusive pathogen. The initial infection is latent. Infection of roots, stolons, underground and aboveground stems begins relatively early in the growing season, but overt symptoms or signs of the pathogen (microsclerotia) may not appear on plants until harvest time. Tubers become infected in the field but may not show obvious symptoms until the middle of the storage period. The disease does not spread from tuber to tuber during long-term storage, but latent infections begin to appear during storage and tuber damage increases. Symptoms of anthracnose are often not clear, unambiguous and coincide with wilting from Alternaria, verticillium, natural aging, nitrogen deficiency, etc. As a result, the identification of the disease and the assessment of its consequences in the growing process are difficult. The impact of the disease on potato yield cannot be predicted, since so many conditions and factors, both biotic and abiotic, affect the harmfulness of the pathogen.
Anthracnose is difficult to control. The inoculum survives in the soil for many years, spreads with planting material and rain, and infection continues throughout the growing season. The longest crop rotation does not clear the soil, and alternating potatoes with crops such as carrots, beets, onions, yellow mustard and rapeseed (for seeds) leads to the accumulation of infection. Minimization of damage from anthracnose is possible on the basis of the full use of organizational and technological measures and the qualified, anti-resistant use of azoxystrobin and a number of other active substances of fungicides. Particular attention should be paid to the level of infection of seed material and soil. It is important to fully and balancedly fertilize and water potatoes, harvest and properly store products in a timely manner, effectively suppress weeds, including weed potatoes, and use the fumigant effect of green manure. Effective fungicides should be alternated and applied when planting in the soil, in the first half of the growing season and before harvesting. The chemical method of anthracnose control should be an obligatory part of a modern potato protection system.
Material author: Sergey Banadysev, Doctor of Agricultural Sciences. Sciences, "Doka-Gene Technologies"