Vegetable Disease Notes:
- Powdery mildew has been reported in a number of tomato greenhouse operations. For control of powdery mildew and other important diseases in greenhouses and high tunnels please see Table E14 on pages E52-E54 of 2016-2017 Commercial Vegetable Production Recommendations Guide.
- A new article on the importance of testing for Dickeya dianthicola in potato seed can be found here.
Damping-off – To help control losses due to damping-off pathogens, apply Ridomil Gold (mefenoxam, FRAC code 4) at 1 to 2 pt/A 4SL, MetaStar (metalaxyl, 4) see label, or azoxystrobin (FRAC code 11) at 0.40 to 0.80 fl oz 2.08SC/1000 row ft (for Rhizoctonia only), or Ridomil Gold at 1.0 to 2.0 pt/A 4SL plus Quadris at 0.40 to 0.80 fl oz 2.08SC/1000 row ft. in a band up to 7 in. after seeding. To help control damping-off pathogens in Collards and Kale only: Apply Uniform (mefenoxam + azoxystrobin, 4 + 11) at 0.34 fl oz 3.66SE/1000 ft row. For more information please see page F32 of the 2016-2017 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Downy Mildew and Alternaria – Symptoms of downy mildew include purple to yellowish-brown spots on upper leaf surfaces. A grayish-white spore mass will develop and cover the underside of leaves under ideal temperatures (night temperatures of 46 to 61oF and day temperatures below 75oF. Downy mildew can kill young plants. Heavily infected leaves may drop providing entry points for bacterial infections (black rot and soft rot). Symptoms of Alternaria on infected leaves include small, expanding circular lesions with concentric rings that may have a ‘shot-hole’ appearance as lesions age. Heavily infected seedlings may result in damping-off. Control of Downy mildew and Alternaria begin with preventative fungicide applications. Please refer to pages F34-35 of the 2016-2017 Mid-Atlantic Commercial Vegetable Production Recommendations Guide to determine which fungicides are labeled for each specific crop and disease.
Bottom Rot/Drop – Spring season is beginning and growers should take precautions to help control Bottom rot (Rhizoctonia) and Lettuce drop (Sclerotinia) which may cause potential problems. For Bottom rot, apply Endura 70W (boscalid, FRAC code 7) at 8.0 to 11.0 oz 70W/A (only 2 applications per season), or iprodione (FRAC code 2) at 1.5 to 2.0 lb 50WP/A or OLF should be applied one week after transplanting or thinning and 10 and 20 days later (only 3 applications per season). For Lettuce drop, apply Endura (FRAC code 7) at 8.0 to 11.0 oz 70WG/A, or iprodione (FRAC code 2) at 1.5 to 2.0 lb/A, or azoxystrobin (FRAC Code 11) at 0.40 – 0.80 fl. oz/1000 row ft 2.08SC, or Cannonball (fludioxonil, 12) at 7.0 oz 50WP/A beginning one week after transplanting or thinning and again at 10 and 20 days later. Uniform (mefenoxam + azoxystrobin, 4 +11) applied at transplanting or seeding will help control damping-off pathogens as well as provide early-season downy mildew control. For more information on control of Bottom rot and Lettuce drop and other important diseases of lettuce. For more information please see 2016-2017 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Bacterial leaf spot and speck – Tomato transplants with suspected symptoms can be treated with streptomycin (Agri-Mycin 17, Agri-Strep, 25) at 1 lb/100 gallons, or 1.25 teaspoon per gallon every 4 to 5 days prior to transplanting. Additionally, Kocide 3000 (copper hydroxide, FRAC code M1) has a greenhouse label for speck and spot control in the greenhouse. Apply ½ to 1.5 TBSP per 1000 sq ft. every 5 to 10 days. Remember, phytotoxicity is an important issue when apply copper in enclosed structures, see label for cautions, restrictions and liabilities.