Disease Control

NOTE: For the disease control products listed below, one product trade name and formulation is provided for each active ingredient (common name) as an example of rates, preharvest interval (PHI), restricted entry interval (REI), and special instructions. In many cases, there are other products available with the same active ingredient. Please see Table 28 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

The symbol OG   indicates a product is listed by the Organic Materials Review Institute (OMRI) as approved for use in organic production. See Organic Certification section for more details.

Seed Piece Treatment (Fungi)

Potato seed treatment is one of the more overlooked portions of a whole-season disease control program. Properly suberized and properly treated seed will provide a better, more uniform stand of plants. Proper application of the appropriate material is necessary. Too much chemical may prove phytotoxic. Inadequate coverage may not totally protect the seed-piece. Dust formulations are preferable for cut seed. CAUTION: Dip treatments may spread bacteria to seed pieces which were previously not affected. NOTE: Many of these seed treatments are now formulated with Douglas fir or alder bark as a carrier. Improved healing of the cut surface has been reported with these products. Some seed treatments can be purchased combined with imidacloprid. Do not use treated seed potatoes for feed or food purposes.

azoxystrobin plus mefenoxam (Quadris Ridomil Gold SL): 0.82 fl oz/100 row feet; REI 0h, Groups 11 & 4.

Bacillus subtilis GB03 (2-3-2 CompanionOG): 1.0 to 2.0 fl oz/gal; PHI 0d, REI 4h, Group NC. For seed cuttings dip. See label for additional application methods.

cymoxanil (Curzate 60 DF): 0.25 to 1.0 oz per hundred weight of cut seed pieces; REI 12h, Group 27. For tuber-borne late blight. Must be applied in a tank mix with another registered product.

fenamidone (Reason 500 SC): 0.15 fl oz/100 lb of seed pieces; REI 12h, Group 11. For seed-borne late blight. See label for application restrictions. NOTE: seed pieces may not be used for food, feed or fodder.

fludioxonil (Maxim PSP): 0.5 lb/100 lb seed-pieces; REI 12h, Group 12. Apply to cover thoroughly.

fludioxonil plus mancozeb (Maxim MZ): 0.5 lb/100 lb.; REI 24h, Groups 12 & M3.

mancozeb  (Dithane F45 Rainshield):  1.6 to 2.5 fl oz/100 lb.; REI 24h, Group M3.

PCNB (Blocker 4F): 5.2 to 10.4 fl oz/1000 row ft.; REI 12h, Group 14. For Rhizoctonia control, apply in 10-20 gallons of water per acre based on a 34-inch row spacing. See label for other application methods and restrictions.

Trichoderma harzianum Rifai Strain KRL-AG2 (RootShield WPOG):  0.03 to 3.0 oz/100 lb seed; REI 0h, Group NC. See label for additional application methods.

Trichoderma harzianum Rifai strain T-22 and T. virens Strain G-41 (RootShield Plus WPOG): 0.03 to 3 lb/100 lb seed; REI 0h, Groups NC. For suppression of Rhizoctonia black scurf and stem canker. Also labeled for in-furrow application. Not effective in cool (below 50°F) and wet soils. See label for additional application methods.

Dickeya, Dickeya black leg (Dickeya dianthicola)

Dickeya dianthicola is a bacterial pathogen within the blackleg complex. In general, Dickeya species are transmitted via seed pieces. Infected seed potatoes are usually non-symptomatic or have non-distinctive rot symptoms. Use sound sanitation practices when handling seed pieces to prevent contamination of other potato lots. The first symptom is poor emergence (skips in a production field) due to rotting seed pieces. Plants that emerge from contaminated seed often wilt and usually have blackened stems that extend upwards from rotting seed piece. Some affected plants may only appear unthrifty. The internal stem tissue may be discolored. Rotations that contain corn followed by brassicas should be avoided prior to planting potatoes. Growers should ensure that they purchase certified seed that has been inspected for Dickeya. Fields where Dickeya has been confirmed should be avoided for the following year. No pesticides are effective for managing Dickeya.

Early Blight (Alternaria solani)  

Crop losses can be heavy if serious defoliation occurs before or soon after flowering. Apply any of the following fungicides when plants are 4" to 6" tall. Begin applications earlier if late blight is found in your area, or if disease forecast systems recommend beginning a protection program. Repeat at 5 to 7 day intervals, depending on amount of moist weather or dew. Use shorter interval under cool (60°F to 70°F) moist conditions. Incorporate diseased vines after harvest and avoid growing pepper, tomato, and potato in a continuous rotation. Allow tubers to mature fully before harvesting, avoid harvesting when the soil is wet, and prevent mechanical injury during harvest and handling. Proper fertilization and mineral balance will reduce susceptibility of plants to early blight. Disease development, based on weather conditions near your farm, can be monitored on-line (www.newa.cornell.edu).

azoxystrobin (Quadris): 6.0 to 15.5 fl oz/A; PHI 14d, REI 4h, Group 11.  Do not make more than one application of Quadris  before alternating with fungicides with a different mode of action.

azoxystrobin plus chlorothalonil (Quadris Opti): 1.6 pt/A; PHI 14d, REI 12h, Groups 11 & M5. See label for tank mix precautions. 

azoxystrobin plus difenoconazole (Quadris Top): 8.0 to 14.0 fl oz/A; PHI 14d, REI 12h, Groups 11 & 3.

Bacillus amyloliquefaciens strain D747 (DoubleNickelOG): 0.25 to 3.0 lb/A; foliar application; PHI 0d, REI 4h, Group 44. For disease suppression only. For improved control; mix or rotate with a chemical fungicide. See label for spray volume calculations.

Bacillus mycoides Isolate J (LifeGardOG): 4.5 oz/100 gal water; PHI 0d, REI 4h, Group P6.

boscalid (Endura 70 WDG): 3.5 to 4.5 oz/A; PHI 10d, REI 12h, Group 7.

chlorothalonil (Bravo Weather Stik): 0.75 pt/A before vines close between rows; 1.0 to 1.5 pt/A after vines close between rows or when disease severity values are reached; PHI 7d, REI 12h, Group M5.

chlorothalonil plus potassium phosphite (Catamaran): 4.0 to 5.5 pt/A; PHI 7d, REI 12h, Groups M5 & 33.

copper hydroxide (Kocide 3000): 0.5 to 1.75 lb/A; PHI 0d, REI 48h, Group M1. Under severe disease, may be tank mixed with other compatible fungicides labeled for potatoes. See label for instructions.

copper oxichloride plus copper hydroxide (Badge X2OG): 1.0 to 4.0 lb/A; PHI 0d, REI 48h, Group M1. Apply higher rate when disease is more severe. Under favorable disease conditions, can tank mix with other compatible fungicide registered for use in potatoes. See label for instructions.

Cymoxanil plus chlorothalonil (Ariston): 2 pt/A; PHI 14d, REI 12h, Group 27 & M5. See label for restricions. Note longer pre harvest interval.

famoxadone plus cymoxanil (Tanos): 6.0 oz/A; PHI 14d, REI 12h, Groups 11 & 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides.

fenamidone (Reason 500 SC): 5.5 to 8.2 fl oz/A; PHI 14d, REI 12h, Group 11. Do not rotate with other Group 11 fungicides.

fluopyram plus pyrimethanil (Luna Tranquility): 11.2 fl oz/A; PHI 7d, REI 12h, Group 7.

fluxapyroxad plus propiconazole (Priaxor): 4.0 to 8.0 fl oz/A; PHI 7d, REI 12h, Groups 7 & 11.

iprodione (Rovral 4F): 1.0 to 2.0 pt/A; PHI 14d, REI 24h, Group 2.

mancozeb (Dithane F45 Rainshield): 0.4 to 1.6 qt/A; PHI 3d, REI 24h, Group M3. See label for application instructions and restrictions. Use of Latron surfactant is recommended.

mancozeb plus copper hydroxide (ManKocide): 1.5 to 5.0 lb/A; PHI 3d, REI 48h, Groups M3 & M1.

mancozeb plus zoxamide (Gavel 75DF): 1.5 to 2.0lb/A; PHI 3d, REI 48h, Groups M3 & 22. Addition of a spreading/penetrating type of adjuvant is recommended. Make no more than 2 consecutive applications before alternating with another fungicide with a different mode of action. 2-3 gallons of spray are generally optimum.

mandipropamid plus difenoconazole (Revus Top): 5.5 to 7.0 fl oz/A; PHI 14d, REI 12h, Group 40 & 3.

metconazole (Quash): 2.5 to 4.0 oz/A; PHI 1d, REI 12h, Group 3.

metiram (Polyram 80 DF): 1.5 to 2.0 lb/100 gal water; PHI 3d, REI 24 h, Group M3. See label for application instructions and restrictions.

polyoxin D (OSO 5% SC): 3.75 to 13.0 fl oz/A; foliar or chemigation; PHI 0d, REI 4h, Group 19. See label for application instructions.

propamocarb (Previcur Flex): 0.7 to 1.2 pt/A; PHI 14d, REI 12h, Group 28. Must be tank mixed with a contact fungicide. See label for rates and timing.  

pyraclostrobin (Headline SC): 6.0 to 9.0 fl oz/A; PHI 3d, REI 12h, Group 11. Do not alternate with other Group 11 fungicides.

pyraclostrobin plus metiram (Cabrio Plus): 2.0 to 2.9 lb/A; PHI 3d, REI 24h, Group 11 & M3.

pyrimethanil (Scala SC): 7.0 fl oz/A; PHI 7d, REI 12h, Group 9.

trifloxystrobin (GEM 500 SC): 2.9 to 3.8 fl oz/A; PHI 7d, REI 12h, Group 11.

trifenyltin hydroxide (Super Tin 80 WP): 1.8 fl oz/A; PHI 7d, REI 48h, Group 30.

Late Blight (Phytophthora infestans)

Late blight can occur from infected seed potatoes or infected tubers overwintered in the field. New strains of P. infestans introduced into the region are resistant to metalaxyl. Do not leave cull piles of potatoes in the field. The fungicides used for early blight have some protective ability against Phytophthora but cannot be relied on to provide significant control. If late blight is reported within 0.5 mile, begin applications of an appropriate fungicide. Disease progression throughout the US can also be monitored (www.usablight.org). Plants with significant disease should be plowed under. Check with your local extension specialist for the availability of special exemption fungicides. Disease development, based on weather conditions near your farm, can be monitored on-line (www.newa.cornell.edu).

ametoctradin plus dimethomorph (Zampro): 11 to 14.0 fl oz/A; PHI 4d, REI 12h, Groups 45 & 40.

azoxystrobin plus chlorothalonil (Quadris Opti): 1.6 pt/A; PHI 14d, REI  12h, Groups 11 & M5. See label for tank mix precautions. 

Bacillus amyloliquefaciens strain D747 (DoubleNickel 55OG): 0.25 to 3.0 lb/A; above ground application; PHI 0d, REI 4h, Group 44. Disease suppression only. For improved control; mix or rotate with a chemical fungicide. See label for other application methods and rates.

Bacillus mycoides Isolate J (LifeGardOG): 4.5 oz/100 gal water; PHI 0d, REI 4h, Group 6. See label to determine concentration for different spray volumes (20-100 gal/A).

chlorothalonil (Bravo Weather Stik): 0.75 pt/A before vines close between rows; 1.0 to 1.5 pt/A after vines close between rows or when disease severity values are reached; PHI 7d, REI 12h, Group M5.

chlorothalonil plus potassium phosphite (Catamaran): 4.0 to 5.5 pt/A; PHI 7d, REI 12h, Groups M5 & 33. Do not apply in a solution having a pH of less than 6.5. See label for tank mix restrictions.

copper hydroxide (Kocide 3000): 0.5 to 1.75 lb/A; PHI 0d, REI 48h, Group M1.  Do not apply in a spray solution having a pH less than 6.5 or tank mix with Aliette. See label for tank mix restrictions.

copper oxychloride plus copper hydroxide (Badge SC): 1.0 to 4.0 lb/A; PHI 0d, REI 48h, Group M1. Apply up to 4lb/A when disease is more severe. Under favorable disease conditions, can tank mix with other compatible fungicide registered for use in potatoes.

cyazofamid (Ranman 400SC): 1.4 to 2.75 fl oz/A; PHI 7d, REI 12h, Group 21. Do not make more than 1 application before alternating with a fungicide with a different mode of action. Addition of an organosilicone surfactant may be desirable.

cymoxanil (Curzate 60 DF): 3.2 oz/A; PHI 14d, REI 12h, Group 27. Use only in combination with a labeled rate of a protectant such as manzate, chlorothalonil or triphenyltin hydroxide.

cymoxanil + chlorothalonil (Ariston): 2.0 pt/A; PHI 14d, REI 12h, Groups 27 & M5. Must be applied in a tank mix with a fungicide with a different mode of action. Do not make more than 2 sequential applications before alternating to a non-Group M5.

dimethomorph (Forum): 4.0 to 6.0 fl oz/A; PHI 4d, REI 12h, Group 40. Must be applied in a tank mix with a fungicide with a different mode of action. Do not make more than 2 sequential applications before alternating to a non-Group 40 fungicide.

famoxadone plus cymoxanil (Tanos): 6.0 to 8.0 oz/A; PHI 14d, REI 12h, Groups 11 & 27. Must be tank mixed with an appropriate contact fungicide with a different mode of action. Do not alternate or tank mix with other Group 11 fungicides.

fenamidone (Reason 500 SC): 5.5 to 8.2 fl oz/A; PHI 14d, REI 12h, Group 11. Do not make more than one application of Reason before alternating to a fungicide with a different mode of action.

fluazinam (Omega 500F): 5.5 fl oz/A; PHI 14d, REI 12h, Group 29. Must be applied in a tank mix with a fungicide with a different mode of action. Do not make more than 2 sequential applications before alternating to a non-group 40.

mancozeb (Dithane F45 Rainshield): 0.4 to 1.6 qt/A; PHI 3d, REI 24h, Group M3.

mancozeb plus copper hydroxide (ManKocide): 1.5 to 5.0 lb/A; PHI 3d, REI 48h, Groups M3 & M1. 

mancozeb plus zoxamide (Gavel 75DF): 1.5 to 2.0 lb/A; PHI 3d, REI 48h, Group M3 & 22. Increase the use rate according to vine development.

mandipropamid plus difenconazole (Revus Top): 5.5 to 7.0 fl oz/A; PHI 14d, REI 12h, Groups 40 & 3. Addition of a spreading/penetrating type of adjuvant is recommended.  Make no more than 2 consecutive applications before alternating with another fungicide with a different mode of action.

mefenoxam plus chlorothalonil (Ridomil Gold Bravo SC): 2.5 pt/A; PHI 14d, REI 48h, Groups 4 & M5.

mefenoxam plus copper (Ridomil Gold Copper): 2.0 lb/A; PHI 14d, REI 48h, Groups 4 & M1. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months.

mefenoxam plus manzate (Ridomil Gold MZ): 2.5 lb/A; PHI 3d, REI 48h, Groups 4 & M3. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months.

oxathiapiprolin plus chlorothalonil (Orondis Opti): 1.75 to 2.5 pt/A; PHI 7d, REI 12h, Groups 49 & M5.

oxathiapiprolin plus mandipropamid (Orondis Ultra): 5.5 to 8.0 fl oz/A; PHI 14d, REI 4h, Groups 49 & 40.

phosphorus acid (Fosphite): 1.0 to 3.0 qt/100 gal; PHI 0d, REI 4h, Group 33. Do not apply to heat or moisture stressed plants. See label for additional precautions.               

propamocarb (Previcur Flex): 0.7 to 1.2 pt/A; PHI 14d, REI 12h, Group 28. Must be tank mixed with a contact fungicide. See label for rates and timing.

pyraclostrobin (Headline): 6.0 to 12.0 fl oz/A; PHI 3d, REI 12h, Group 11.  Do not rotate with other Group 11 fungicides.

pyraclostrobin plus metiram (Cabrio Plus): 2.9 lb/A; PHI 3d, REI 24h, Group 11 & M3.

trifloxystrobin (GEM 500 SC): 3.8 fl oz/A; PHI 7d, REI 12 h, Group 11. Must be tank mixed with a protectant.

triphenyltin hydroxide (Super Tin 80 WP): 1.87 oz/A; PHI 7d, REI 48h, Group 30.

zoxamide plus chlorothalonil (Zing!): 32.0 to 34.0 fl oz/A; PHI 7d, REI 12h, Groups 22 & M5.

Common Scab (Streptomyces spp.)

Scab is caused by the soilborne bacterium Streptomyces scabies. The disease tends to be prevalent when soil is dry during tuber initiation, soil pH is above 5.2, and non-decomposed manure is used as fertilizer. Continuous cropping of potato will also increase the disease. When planting susceptible varieties, avoid fields with a history of scab. When scab is present, rotate out of potatoes for at least 2 years. Beets, carrots, radish and some weeds can also be hosts. Maintain soil pH at 5 to 5.2. The varieties Norchip, Norland, Pike, Salem and Superior are resistant to scab. Allegany, Andover, Atlantic, Chieftain, Elba, Genesee, Monoma, Reba and Redsen are moderately resistant. Katahdin, Kennebec and Snowden are moderately susceptible. Chippewa, Kanona, Norwis and Yukon Gold are very susceptible.

Pythium Leak or shell rot (Pythium spp.)

Leak can be a problem in stored potatoes, especially bruised, immature potatoes harvested in hot weather.

mefenoxam (Ridomil Gold SL): 0.42 oz/1,000 linear ft (in furrow); REI 0, Group 4. Apply as a 6-8 inch band at planting in a minimum of 3 gal of water. See label for pre-plant incorporated application rates. Can be supplemented with a phosphorous acid product. See label for details. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months. 

mefenoxam plus chlorothalonil (Ridomil Gold Bravo SC): 2.5 pt/A; PHI 14d, REI 48h, Groups 4 & M5.  Apply as a 6-8 inch band at planting in a minimum of 3 gal of water. Can be supplemented with a phosphorous acid product. See label for details. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months. 

mefenoxam plus copper (Ridomil Gold Copper): 2.0 lb/A; foliar applied. PHI 14d, REI 48h, Groups 4 & M1. Apply as a 6-8 inch band at planting in a minimum of 3 gal of water. Can be supplemented with a phosphorous acid product. See label for details. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months.

mefenoxam plus manzate (Ridomil Gold MZ): 2.5 lb/A; PHI 3d, REI 48h, Groups 4 & M3. Apply as a 6-8 inch band at planting in a minimum of 3 gal of water. Can be supplemented with a phosphorous acid product. See label for details. Do not plant any crop which is not registered for use with Ridomil Gold active ingredient in treated soil for a period of 12 months.

phosphorus acid (Phostrol): 3.75 to 10 pt/A; in furrow or 2.5 to 10 pt/A foliar applied; PHI 0d, REI 4h, Group P7. For suppression of leak, combine the in-furrow treatment of phosphorous acid with a mefenoxam fungicide (Group 4). Additional in-season foliar applications of a phosphorous acid containing fungicide tank mixed with a mefenoxam containing fungicide may be necessary to achieve adequate control. See labels for specific rates.

Verticillium and Fusarium Wilt

Verticillium and Fusarium are soil-borne fungi that cause vascular wilts of potato. They can be introduced into fields by contaminated seed or soil. Continual potato production tends to result in an increase in wilt disease. A combination of lesion nematodes and Verticillium results in early death. Rotation with non-susceptible crops such as grasses will reduce disease. Destruction of infected potato vines by tillage encourages rapid decomposition and lessens the build-up of soil inoculum. At this time, there are no varieties resistant to Fusarium Wilt. Avoid highly susceptible cultivars and start with certified, disease-free seed pieces.

Trichoderma asperellum, T. gamsii (Bio-tam 2.0OG): See label for in-furrow, drench, and broadcast rates; REI 1h, Group NC.

Potato Leaf Roll Virus (PLRV)

Virus control will be enhanced by buying certified seed. Consult seed producers to determine what the certification covers. Destroy cull piles and volunteer plants. Potato Leaf Roll Virus is the most serious virus disease of potatoes in New England and can result in significant yield reductions. The virus is transmitted by aphids in a persistent manner. The virus can overwinter in unharvested tubers which may develop into virus-infected volunteer plants. Plant virus-free, certified seed. Remove volunteer plants. Rogue plants with virus symptoms. When populations of aphids reach economic thresholds, treatment is warranted. Do not use any of last year's potato harvest for seed.

Potato Virus S (PVS), Potato Virus A (PVA), Potato Virus X (PVX)

Virus control will be enhanced by buying certified seed. Consult seed producers to determine what the certification covers. Destroy cull piles and volunteer plants. Do not keep potatoes for seed. These viruses may occur singly or in combination. PVY, PVS and PVA are spread by aphids in a nonpersistent manner. PVX is not known to be spread by aphids but is easily spread by plant-to-plant contact, farm machinery or cultural practices. Plant certified virus-free seed. Plant early, use resistant varieties, and control aphid populations.

Potato Virus Y

Potato Virus Y (PVY) has a worldwide distribution and is one of the most important viruses affecting potato. Three main strains have been described that differ in distribution and symptomatology. Symptoms vary widely with cultivars and virus strain combinations, ranging from mild mosaic to severe foliar necrosis. One strain can cause a symptomless current season infection that leads to next-generation infection. Primary symptoms of PVY include mottling, yellowing, leaf drop, and premature plant death. Potato with secondary infection exhibit stunting, mottling, stem necrosis, and crinkled leaves. Symptoms may be suppressed by low or high temperatures. Tuber symptoms generally correspond to leaf effects. PVY is the type member of the plant virus family Potyviridae, the largest and most significant virus group, and has caused significant losses in agricultural, forage, and horticultural crops. Hosts include Solanaceous, Leguminous, and Chenopodiaceae (i.e. spinach, chard, beets) families. Infection is transmitted in a non-persistent manner by more than 25 species of aphids and may also occur mechanically by foliar or tuber contact. Long distance transport is by winged aphids Use certified, disease-free seed tubers to reduce primary inoculum. Insecticides may slow the spread of disease within a crop, but may actually increase insect probing and be counterproductive because only a few seconds of insect feeding is sufficient for virus transmission. Minimize contact disease spread by minimizing mechanical damage during cultivation, spraying, and harvest. Sanitize seed cutting equipment between seed lots. Remove virus-infected plants. Resistant cultivars are available.