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 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.

Anthracnose (Colletotrichum), Alternaria, and Black Rot (Didymella)

 Do not plant winter squash or pumpkins for at least two years in fields where these diseases have been a problem. Plow under plant debris after harvest. Reduce weeds to allow for faster drying of plant surfaces. Start with certified disease-free seed. Carefully scout transplant greenhouse for diseased plants and remove them, improve ventilation in greenhouse, and reduce overhead irrigation. Avoid injuring fruit before or during harvest.  Apply protectant fungicides according to a disease forecasting system (Melcast). Black rot is one of the most destructive diseases of winter squash and pumpkins. Cultivars with resistance to Anthracnose are available.

azoxystrobin (Quadris): 11.0 to 15.5 fl oz/A. (1 dh, REI 4h, Group 11). Do not alternate with other Group 11 fungicides. Resistant isolates of Black Rot (Didymella) have been reported.

azoxystrobin plus chlorothalonil (Quadris Opti): 3.2 pt/A. (1 dh, REI 12h, Groups 11 & M5). See label for tank mix precautions.  

azoxystrobin plus difenoconazole (Quadris Top): 12.0-14.0 fl oz/A. (1 dh, REI 12h, Groups 11 & 3). 

boscalid (Endura): 6.5 oz/A. (0 dh, REI 12h, Group 7).

Bacillus mycoides Isolate J (LifeGardOG): 4.5 oz/100 gal water. (0 dh, REI 4, Group 44).

chlorothalonil (BravoWeather Stik): 1.5 to 3.0 pt/A. (0 dh, REI 12h, Group M5). Bravo can cause injury to watermelon fruit; see label. For other products, see labels.

chlorothalonil plus oxathiapiprolin (Orondis Opti):  1.7 to 2.5 pt/A. (0 dh, REI 12h, Groups M5 & U15).

chlorothalonil plus potassium phosphite (Catamaran): 4 pt/A. (0 dh, REI 12, Groups M5 & 33).

copper hydroxide (Kocide 3000): 0.5-1.25 lb/A. (0 dh, REI 48h, Group M1). Discontinue use if crop injury occurs.  Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. Not labeled for gourds.

cyprodinil plus fludioxonil (Switch 6.25 WG): 11.0-14.0 oz/A. (1 dh, REI 12h, Groups 9 & 12).

cymoxanil plus chlorothalonil (Ariston): 1.9 to 3 pt/A. (3 dh, REI 12h, Groups 27 & M5).  

difenoconazole plus cyprodinil (Inspire Super): 16 to 20 fl oz/A. (7 dh, REI 12h, Group 3 & 9). Apply in sufficient volume to achieve thorough coverage. Do not use for the control of gummy stem blight.

famoxadone plus cymoxanil (Tanos): 8.0 oz/A. (3 dh, REI 12h, Groups 11 & 27). Tank mix with an appropriate contact fungicide with a different mode of action.

fenamidone (Reason 500 SC): 5.5 fl oz/A. (14 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides. For Alternaria and downy mildew only.

flutriafol (Rhyme 2.08 SC): 5-7 fl oz/A. (o ph, REI 12h, Group 3). For gummy stem blight only.

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. (5 dh, REI 48h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. Not for gummy stem blight.

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

pyraclostrobin (Cabrio EG): 12 to 16 oz/A. (0 dh, REI 12h, Group 11). Do not make more than one application of Cabrio before alternating to a labeled fungicide with a different mode of action.

pyraclostrobin plus boscalid (Pristine): 12.5 to 18.5 oz/A. (0 dh, REI 12h, Groups 11 & 7). Use caution in the addition of adjuvants or additives (see label).

thiophanate-methyl (Topsin M 70Wp):  0.5 lb/A. (1 dh, REI 24h, Group 1). The repeated exclusive use of Topsin M may lead to buildup of resistant strains of fungi and loss of disease control. Tank mix with chlorothalonil.

Downy Mildew (Pseudoperonospora cubensis)

Pseudoperonospora cubensis infects only members of the cucurbit family and is an obligate parasite. Its survival depends on the presence of cucurbit hosts, either in climates which permit their growth year round or in greenhouse culture. The source of primary inoculum in cold climates is windblown sporangia from areas where plants survive the cold season. Generally, Downy mildew of cucurbits does not arrive in southern New England until September. However, in some seasons it can move up the eastern seaboard early and arrive in July. The progress of Downy mildew is tracked by the North American Plant Disease Forecast Center and warnings issued based on disease progression and weather ( http://cdm.ipmpipe.org/).  Physiological specialization occurs in P. cubensis and at least 5 pathotypes have been described. Cucumber and melon are susceptible to all pathotypes, while squash and melon cultivars vary in their reactions. Spread of Downy mildew within a field can be by air currents, rain splash, workers, and tools. The main means of control are fungicide applications, the use of resistant cultivars, and cultural practices. Maximum control can be achieved only with a combination of these measures. Maximize the distance from potential inoculum sources. Use plant spacings which reduce the density of the plant canopy. Avoid overhead irrigation. Both these practices are aimed at minimizing the length of leaf wetness periods. Squash and pumpkin cultivars are resistant to some pathotypes but are very susceptible to compatible pathotypes.

ametoctradin plus dimethomorph (Zampro): 14.0 fl oz/A. (0 dh, REI 12h, Groups 45 & 40).

Bacillus mycoides Isolate J (LifeGardOG): 4.5 oz/100 gal water. (0 dh, REI 4, Group 44).

chlorothalonil (Bravo Weather Stik): 1.5 to 2.0 pt/A. (0 dh, REI 12h, Group M5).

chlorothalonil plus oxathiapiprolin (Orondis Opti):  1.7 to 2.5 pt/A. (0 dh, REI 12h, Groups M5 & U15).

copper hydroxide (Kocide 3000): 0.5-1.25 lb/A. (0 dh, REI 48h, Group M1). Discontinue use if crop injury occurs. Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

cyazofamid (Ranman): 2.1 to 2.75 fl oz/A. (0 dh, REI 12h, Group 21).  Tank mix with an organosilicone surfactant or non-ionic surfactant. Alternate sprays of Ranman with a fungicide with a different mode of action.

cymoxanil (Curzate 60 DF): 3.2 to 5.0 oz/A. (3 dh, REI 12h, Group 27). Use only in combination of a labeled rate of a protectant fungicide (copper, chlorothalonil).

cymoxanil plus chlorothalonil (Ariston): 1.9 to 3 pt/A. (3 dh, REI 12h, Groups 27 & M5).

dimethomorph (Forum): 6 oz/A. (0 dh, REI 12h, Group 40). Apply only in combination with a labeled rate of another non-group 40 fungicide. Do not make more than two sequential applications of Forum before alternating to a fungicide with a different mode of action.

famoxadone plus cymoxanil (Tanos ): 8 oz/A. (3 dh, REI 12h, Groups 11 & 27).Tank mix with an appropriate contact fungicide.

fenamidone (Reason 500 SC): 5.5 fl oz/A. (14 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides. For Alternaria  and downy mildew only.

fluopicolide (Presidio 4F): 3 to 4 fl oz/A. (2 dh, REI 12h, Group 43). Must be tank mixed with another fungicide with a different mode of action.

fosetyl Al (Aliette 80 WDG): 2 to 5 lb/A. (12 dh, REI 12h, Group 33).  Do not tank mix with copper.

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. (5 dh, REI 48 h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

oxathiapiprolin (Orondis Ultra A): 2.0 to 4.8 fl oz/acre (0 ph, REI 4, Group U15).

phosphorous 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. Copper phytotoxicity may occur if applied in alteration with copper.

propamocarb HCl (Previcur Flex): 1.2 pt/A. (2 dh, REI 12h, Group 28). Alternate with a contact fungicide (copper, chlorothalonil, sulfur).

pyraclostrobin (Cabrio EG): 8 to 12 oz/A. (0 dh, REI 12h, Group 11). Do not make more than one application before alternating with a non-Group 11 fungicide.

zoxamide + chlorothalonil (Zing!): 36 fl oz/A. ( 0 ph, REI 12h, Groups 22 & M5).

zoxamide plus mancozeb (Gavel): 1.5 to 2 lb/A. (5dh, REI 48, Groups 22 & M3). Do not tank mix Gavel with another M3 fungicide if the target pest is only downy mildew. Tank-mix only if a partner is required to control other diseases, such as copper for bacterial disease.

Phytophthora Blight and Fruit Rot

Phytophthora capsici cannot be managed by fungicide applications alone; successful disease control is achieved only by a season-long effort to manage water and other cultural practices. The single most effective way to control this disease is to prevent its movement into clean fields by equipment, humans, or infested water. Plant susceptible crops (tomatoes, peppers, eggplant, and all cucurbit species) in fields that have no history of this disease and are well-drained (lima beans have also been reported as susceptible). Plant non-vining crops on raised beds, avoid planting in low areas where water puddles, and improve drainage by sub-soiling after heavy rain events. Promptly disk under small areas where the disease appears along with a border of healthy appearing plants. Avoid working in wet fields and compacting the soil.

ametoctradin plus dimethomorph (Zampro): 14.0 fl oz/A. (0 dh, REI 12h, Groups 45 & 40).

cyazofamid (Ranman): 2.75 fl oz/A. (0 dh, REI 12h, Group 21). Mix with a surfactant for best results. Alternate sprays of Ranman with a fungicide with a different mode of action.

dimethomorph (Forum): 6 fl oz/A. (0 dh, REI 12h, Group 40). Apply only in combination with a labeled rate of another non-group 40 fungicide. Do not make more than 2 sequential applications of Forum before alternating to a fungicide with a different mode of action.

famoxadone plus cymoxanil (Tanos): 8 to 10 oz/A. (3 dh, REI 12h, Groups 11 & 27). For SUPPRESSION of foliar and fruit phase ONLY. Tank mix with an appropriate contact fungicide with a different mode of action (copper or chlorothalonil).

fosetyl-Al (Aliette WDG): 2 to 5 lb/A. (0 dh, REI 12h, Group 33).Do not tank mix with copper compounds. Use the high rate when Phytophthora blight is active.

fluopicolide (Presidio): 3 to 4 fl oz/A. (2 dh, REI 12h, Group 43). Must be tank mixed with another fungicide with a different mode of action.

phosphorous 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. Copper phytotoxicity may occur if applied in alteration with copper.

Plectosporium Blight (Plectosporium tabacinum)

When Plectosporium blight occurs, rotate away from summer squash and pumpkins for 2 years. Choose sunny, well-drained sites for planting cucurbits. Scout for disease and apply fungicides when disease first occurs. Thorough coverage of foliage, vines, and fruit is necessary for good control. The Strobilurin (QoI) fungicides Flint (trifloxystrobin), Cabrio (pyraclostrobin), and Quadris (azoxystrobin) will control this disease but should not be rotated with each other or the pathogen will develop resistance. Apply a protectant fungicide such as chlorothalonil (Bravo) or mancozeb (Dithane) following a strobilurin.

azoxystrobin plus difenoconazole (Quadris Top): 12.0-14.0 fl oz/A. (1 dh, REI 12h, Groups 11 & 3).

difenoconazole plus cyprodinil (Inspire Super): 16 to 20 fl oz/A. (7 dh, REI 12h, Group 3 & 9). Apply in sufficient volume to achieve thorough coverage.

floxapyroxad plus pyraclostrobin (Merivon): 4 to 5.5 fl oz/A. (0 dh, REI 0.5, Groups 7 & 11). Make no more than two sequential applications before alternating with fungicides that have a different mode of action.

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. (5 dh, REI 48h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

pyraclostrobin (Cabrio EG): 12 to 16 oz/A. (0 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides such as Quadris or Flint.

trifloxystrobin (Flint): 1.5 to 2.0 oz/A. (0 dh, REI 12h, Group 11). Do not rotate with other Group 11 fungicides such as Quadris or Cabrio.

Post-Harvest Fruit Rot (Various Fungi)

Fruit and stem rot that develops after harvest is generally due to infection that took place in the field. Postharvest rot can be reduced by applying fungicides during the growing season on a regular basis, as for control of black rot. Control weeds to allow better air circulation. Wounds to the fruit that occur during harvest can also result in postharvest rot. For maximum storage life, refer to Harvest and Storage in the Cultural Practices section.

Powdery Mildew (Podosphaera xanthii)

Fungicides should be applied at the first sign of disease. For cucurbits, this is often as late as August but scouting should begin in July. On cucurbits, powdery mildew fungi attack both the top and bottom of the leaf, and this makes the disease more difficult to control with non-systemic fungicides. However, powdery mildew fungi tend to become resistant to systemic fungicides such as Topsin-M, Nova, Cabrio, Flint and Quadris. Cabrio, Flint and Quadris are strobilurins and have the same mode of action so they should not be rotated with each other. Resistance to strobilurins has resulted in the removal of this class of fungicides from recommendations, with the exception of Pristine which is a combination product. Resistance to the DMI fungicides (Rally, Procure) is also widespread; use Rally or Procure at the high labeled rate only.

Bacillus amyloliquefaciens strain D747 (DoubleNickelOG): 0.25 to 3.0 lb/A. (0 dh, REI 4 h, Group 44). Disease suppression only. For improved control; mix or rotate with a chemical fungicide.

Bacillus subtilis (Serenade MaxOG): 1 to 3 lb/A. (0dh, REI 4h, Group 44). Provides limited, contact control. Thorough coverage is necessary. Consider mixing with another contact fungicide.

Bacillus mycoides Isolate J (LifeGardOG): 4.5 oz/100 gal water. (0 dh, REI 4, Group 44).

botanical extract (RegaliaOG)): 1 to 4 qt/A. (0dh, REI 4h, Group P). Apply to assure thorough coverage.

botanical oil [neem] (Trilogy): 0.5-1% solution/A. (0 ph, REI 4h, Group NC).

chlorothalonil (Bravo Weather Stik): 2 to 3 pt/A. (0 dh, REI 12h, Group M5). Powdery mildew will not become resistant to Bravo but it is not systemic so coverage is critical.

copper hydroxide (Kocide 3000): 0.5-1.25 lb/A. (0 dh, REI 48h, Group M1). Discontinue use if crop injury occurs. Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

cyflufenamid (Torino): 3.4 oz/A. (0 dh, REI 4h, Group U6).

cyprodinil plus fludioxonil (Switch 6.25 WG): 11.0-14.0 oz/A. (1 dh, REI 12h, Groups 9 & 12).

cymoxanil plus chlorothalonil (Ariston): 1.9 to 3 pt/A. (3 dh, REI 12h, Groups 27 & M5).    

difenoconazole plus cyprodinil (Inspire Super): 16 to 20 fl oz/A. (7 dh, REI 12h, Group 3 & 9). Apply in sufficient volume to achieve thorough coverage.

flutriafol (Rhyme 2.08 SC): 5-7 fl oz/A. (o ph, REI 12h, Group 3).

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. ( 5 dh, REI 48h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

metrafenone (Vivando): 15.4 fl oz/A. (0dh, REI 12h, Group U8).

mineral oil (JMS Stylet-OilOG): 3 to 6 qt/100 gal water. (0dh, REI 4h, Group NC).

monopotassium phosphate (Nutrol): 8 to 12 lb/A (0dh, REI 4h, Group NC).

myclobutanil (Rally):  2.5 to 5 oz/A. (0 dh, REI 24h, Group 3). Observe a 30-day plant back interval.

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

penthiopyrad (Fontelis): 14.2 to 16.0 fl oz/A. (1 dh, REI 12h), Group 7).

potassium bicarbonate (KaligreenOG): 2.5 to 5.0 lb/A. (1dh, REI 0h, Group NC).

pyraclostrobin plus boscalid (Pristine): 12.5 to 18.5 oz/A. (0 ph, REI 12h, Groups 11 & 7).

quinoxyfen (Quintec): 4 to 6 fl oz/A. (3 dh, REI 12h, Group 13). Tank mix with a protectant fungicide. Alternate with a non-Group 13 fungicide. 

sulfur (Microthiol Disperss): 5 to 10 lb/A. (0 dh, REI 24h, Group M2). Sulfur can injure plants, especially when temperatures reach 90° F. Do not apply to sulfur sensitive varieties.

triflumizole (Procure 50WS): 4 to 8 fl oz/A. (0 dh, REI 12h, Group 3).

Scab (Cladosporium cucumerinum)

Scab is a significant problem for summer and winter squash, pumpkin, melon, and watermelon. Resistant cultivars of cucumber are widely available. Where Scab has been a problem, plant in sunny locations where cool air does not tend to accumulate. The pathogen survives in the soil on infected crop debris, may be seedborne, and is capable of saprophytic growth.  Rotate with non-cucurbit crops for 2-3 years. Select sites with well-drained soil and good air movement for rapid drying of foliage and fruit.  Avoid overhead irrigation and dense plant canopies.  Fungicide sprays may not be effective during extended cool, wet weather due to the short disease cycle of this pathogen.

chlorothalonil (Bravo Weather Stik): 2.0-3.0 lb/A. (0 dh, REI 12h, Group M5). Use caution when applying to watermelon: see label).

chlorothalonil plus potassium phosphite (Catamaran): 6 pt/A. (0 dh, REI 12, Groups M5 & 33).

mancozeb (Dithane F45):  1.6-2.4 qt/A. (5 dh, REI 24h, Group M3).

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. (5 dh, REI 48h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

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

Angular leaf spot (Pseudomonas lachrymans)

Angular leaf spot is not usually a serious disease in New England. Plow under crop residue after harvest. Rotate away from cucurbits for at least one year.

copper hydroxide (Kocide 3000): 0.5-1.25 lb/A. (0 dh, REI 48h, Group M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette. Discontinue use if crop injury occurs.

mancozeb plus copper hydroxide (ManKocide): 2.0-3.0 lb/A. (5 dh, REI 48h, Groups M3 & M1). Do not apply in a spray solution having a pH of less than 6.5 or tank mix with Aliette.

Bacterial Wilt (Erwinia tracheiphila)

Because this bacterium is transmitted systemically by cucumber beetles, copper sprays are of no value. Cucumber beetles must be controlled by appropriate insecticide programs. Scout twice weekly at seedling stage for cucumber beetles. Treat when beetle numbers reach the threshold of 1 beetle per 100 feet of row. Use crop rotation to reduce beetle numbers. Rogue infected plants. Spunbonded row covers will exclude beetles. Plant a sprayed perimeter trap crop of Blue Hubbard squash to protect more susceptible crops. 

Cucurbit Viruses: CMV, WMV-II, PRSV-W and ZYMV

Refer to the discussion of these viruses in the section in Cucumber, Muskmelon and Watermelon.