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 61°F and day temperatures below 75°F. 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 2015 NJ Commercial Vegetable Production Recommendations to determine which fungicides are labeled for each specific crop and disease.
Bacterial leaf blight – Symptoms include numerous black, irregular ‘greasy’ lesions on leaves and can be problematic when overhead irrigation has been used extensively. The bacterium can survive on weeds and infected debris left in the field. Abandoned plantings should be thoroughly worked back into the soil to allow decomposition of infected plants. Copper fungicide applied on a regular basis may help to suppress the spread of the disease.
Anthracnose – Symptoms in spinach are small, circular, water‑soaked lesions on both young and old leaves. Lesions later enlarge, turn brown to tan in color, and become thin and papery. In severe cases, lesions coalesce and result in severe blighting of foliage. Avoid excessive overhead irrigation if possible.
Alternate the following fungicides:
Fontelis (penthiopyrad, 7) at 24.0 fl oz 1.67SC/A with
Cabrio (pyraclostrobin, 11) at 12.0 to 16.0 oz 20EG/A
If more than 2 applications are needed apply:
Merivon (fluxapyroxad + pyraclostrobin, 7 + 11) at 4.0 to 11.0 fl oz 2.09SC/A
Pristine (boscalid + pyraclostrobin, 7 +11) at 18.5 oz 38EG/A