August 16th

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Vegetable Diseases Updates:

Rhubarb Leaf Spot. Severe leaf spot of rhubarb, caused by the fungus Ascochyta rhei, was observed in a commercial field in southwest Illinois. This disease has previously been diagnosed on the leaves collected from home gardens and commercial rhubarb fields. The first indication of Ascochyta leaf spot are small, yellow-green spots in the upper leaf surfaces. In less than a week, the invaded tissue usually turns brown and dies, resulting in circular to angular spots that vary in size. Fruiting bodies of the pathogen are rarely visible in the spots. When the affected tissue dies, it may drop out, leaving large ragged holes in the leaves. To control rhubarb leaf spot, plant residue in gardens should be gathered and destroyed as soon as the first frost kills them. In commercial fields, growers should thoroughly incorporate the crop residues between the rows after harvest. During the harvest in the spring, those with spotted leaves should be taken first, as much of the diseased material can be removed by this method. Rhubarb plants should be fertilized as soon as growth starts in the spring and another application should be made as soon as the harvest is completed to encourage strong, rapid growth. Quadris has been registered for control of rhubarb leaf spots.

Rhubarb Crown Rot. Crown rot of rhubarb was observed in one commercial field in southwest Illinois. The pathogen growing on the infected crowns was Rhizoctonia. Crown rot is occasionally a problem in rhubarb, especially under wet soil conditions. Phytophthora, Pythium, and Rhizoctonia species may cause crown rot of rhubarb. Infection usually occurs at the base of the stalks or a little below the soil surface. Stalk lesions are brown and sunken. Rotted crown tissue is usually firm and brown, but may turn mushy if bacterial soft rot ensues. Leaves wilt and die, usually a few at a time, and severely infected plants eventually die. To manage crown rot of rhubarb, planting should be established in well-drained, fertile, weed-free fields. Rhubarb should not be planted immediately after other vegetable crops in the rotation.

Gravel -New Fungicide. A new fungicide (Gravel) for disease control in cucurbits, potatoes, and tomatoes is now available. Gavel (8.3% zaxomide + 66.7% mancozeb), manufactured by Dow AgroSciences, is a protectant compound, effective against foliar diseases of cucurbits (cucumber, melons, summer squash, and watermelon), potatoes, and tomatoes. Gavel can be used to control cucurbit diseases (Alternaria leaf spot, Cercospora leaf spot, downy mildew, and fruit and stem rot), potato diseases (early blight and late blight), and tomato diseases (Buckeye rot, early blight, Gray leaf spot, late blight, Septoria leaf spot, bacterial speck, and bacterial spot). Gavel may be applied by ground or air at a maximum rate of 2.0 pounds product (1.5 lb active ingredient) per acre. Number of applications and preharvest interval vary with crop. Read and follow label directions.

 

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