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, days to harvest (dh), REI, and special instructions. In many cases there are other products available with the same active ingredient. Please see Table 27 and Fungicides and Bactericides Alphabetical Listing by Trade Name for more information on products with the same active ingredients.

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.

Bacillus subtilis GB03 (Companion Liquid Biological FungicideOG): 1.0 to 2.0 fl oz/gal. (Group NC)

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

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

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

Trichoderma harzianum Rifai strain KRL-AG2 (RootShield WPOG):  0.3 to 3.0 oz/100 lb seed. (Group NC).

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.

azoxystrobin (Quadris): 6.0 to 15.5 fl oz/A. (14 dh, 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. (14 dh, REI 12h, Groups 11 & M5). See label for tank mix precautions. 

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

boscalid (Endura): 2.5 to 4.5 oz/A. (10 dh, REI 12h, Group 7).

chlorothalonil (Bravo Weather Stik): 0.75 pt/A before vines close between rows; 1 to 1.5 pt/A after vines close between rows or when disease severity values are reached (7 dh, REI 12h, Group M5).

difenoconazole (Inspire): 4.0-7.0 fl oz/A. (14 dh, REI 12h, Group). Apply in sufficient volume to achieve thorough coverage.

famoxadone plus cymoxanil (Tanos): 6.0 oz/A. (14 dh, 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 fl oz/A. (14 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides. 

fluopyram (Luna Privilege): 4.0-5.47 fl oz/A. (7 dh, REI 12h, Group 7).

fluopyram plusprimethanil (Luna Tranquility): 11.2 fl oz/A. (7 dh, REI 12h, Group 7).

iprodione (Rovral 4F): 1.0-2.0 pt/A. (14 dh, REI 24h, Group 2).

mancozeb (Dithane F45): 0.4-1.6 qt/A. (3 dh, REI 24h, Group M3).

mancozeb plus copper hydroxide (ManKocide): 1.5-5.0 lb/A. (3 dh, REI 48h, Groups M3 & M1).  

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

polyoxin D (OSO 5% SC): 3.75-13.0 fl oz/A. (0 dh, REI 4h, Group 19).

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

pyraclostrobin (Headline): 6 to 9 fl oz/A. (3 dh, REI 12h, Group 11). Do not alternate with other Group 11 fungicides.

pyraclostrobin plus metiram (Cabrio Plus): 2.0-2.9 lb/A. (3 dh, REI 24h, Group 11 & M3).

pyrimethanil (SCALA SC): 7 fl oz/A. (7 dh, REI 12h, Group 9).

zoxamide plus mancozeb (Gavel 75 DF): 1.5-2.0 lb/A. (3 dh, REI 48h, Groups 22 & M3). 

Late Blight (Phytophthora infestans)

Late blight can occur from infected seed potatoes or infected tubers overwintered in the field. New late blight strains introduced into the region are resistant to metalaxyl. Do not leave cull pules 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. Plants with significant disease should be plowed under. Check with your local extension specialist for the availability of special exemption fungicides.

ametoctradin plus dimethomorph (Zampro): 14.0 fl oz/A. (4 dh, REI 12h, Groups 45 & 40).

azoxystrobin (Quadris): 12.0 fl oz/A. (14 dh, 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. (14 dh, REI  12h, Groups 11 & M5). See label for tank mix precautions.  

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

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

cyazfamid (Ranman): 1.4 to 2.75 fl oz/A. (7 dh, 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. (14 dh, REI 12h, Group 27). Use only in combination with a labeled rate of a protectant such as manzate, chlorothalonil or triphenyltin hydroxide.

dimethomorph  (Forum): 6 fl oz/A. (4 dh, 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 to 8 oz/A. (14 dh, 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. (14 dh, 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. (14 dh, REI 48h,Group 29).

mancozeb (Dithane F45): 0.4-1.6 qt/A. (3 dh, REI 24h, Group M3).

mancozeb plus copper hydroxide (ManKocide): 1.5-5.0 lb/A. (3 dh, REI 48h, Groups M3 & M1). 

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

mandipropamid plus difenconazole (Revus Top): 5.5 to 7.0 fl oz/A. (14 dh, 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. (14 dh, REI 48h, Groups 4 & M5).  

mefenoxam plus copper (Ridomil Gold Copper): 2.0 lb/A. (14 dh, 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. (3 dh, 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.                                                                                                                                          

potassium salts of phosphoric acid (Fosphite): 1.0-3.0 qt/100 gal. (0 dh, REI 4h, Group 33). Do not apply to heat or moisture stressed plants. Do not apply to plants treated with copper compounds within the last 20 days.                                                                                                                              

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

pyraclostrobin (Headline): 6 to 12 fl oz/A. (3 dh, REI 12h, Group 11).  Do not rotate with other Group 11 fungicides.

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

Common Scab (Streptomyces)

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 two years. Beets, carrots, radish and some weeds can also be hosts. Maintain soil at 5 to 5.2. Mancozeb may be useful in controlling seed-borne scab. The varieties Norchip, Norland, Pike, Salem and Superior are resistant to scab. Allengany, 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

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

azoxystrobin plus mefenoxam (Quadris Ridomil Gold):  0.82 fl oz/1000 ft row. (REI 0h, Groups 11 & 4). Soil incorporated.

mefenoxam plus chlorothalonil (Ridomil Gold Bravo SC): 2.5 pt/A. (14 dh, REI 48h, Groups 4 & M5).  Do not plant any crop which is not registered for use with Ridomil Gold EC active ingredient in treated soil for a period of 12 months. 

mefenoxam plus copper (Ridomil Gold Copper): 2.0 lb/A. (14 dh, REI 48h, Groups 4 & M1).

mefenoxam plus manzate (Ridomil Gold MZ): 2.5 lb/A. (3 dh, 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.

potassium salts of phosphoric acid (Fosphite): 1.0-3.0 qt/100 gal. (0 dh, REI 4h, Group 33). Do not apply to plants that are heat or moisture stressed or recently treated with copper.

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 dying. Rotation with nonsusceptible 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-tamOG): 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 virus-free certified 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 Chenopodiiaceae (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.