The following plant disease highlights have been compiled from samples submitted to the University of Kentucky Plant Disease Diagnostic Laboratories from August 1 to August 17, 2020.
Diagnostic samples of agronomic crops have included Rhizoctonia root and crown rot, Rhizoctonia web blight, spring black stem and leaf spot, summer black stem and leaf spot, and anthracnose on alfalfa; leaf streak on orchardgrass; Cercospora and Septoria leaf spots on hemp; gray leaf spot, Diplodia leaf streak, northern corn leaf blight, southern rust, common rust, Curvularia leaf spot, and physiological spotting on corn; Phytophthora rot/stem rot, sudden death syndrome, target spot, frogeye leaf spot, brown spot, downy mildew, charcoal rot, and potassium deficiency on soybean; black shank, soreshin, angular leaf spot, frogeye leaf spot, target spot, brown spot, alfalfa mosaic virus, potyvirus, and potassium and boron deficiencies on tobacco.
On fruit, vegetable, and herb crops, we have diagnosed frogeye leaf spot, bitter rot, and plum curculio injury on apple; brown rot on peach; Rhizoctonia web blight on bean; gray leaf spot, northern corn leaf blight, southern rust, and common smut on sweet corn; anthracnose, Cercospora leaf spot, powdery mildew, and downy mildew on cucumber; Phytophthora fruit rot on gourd; Pythium and Rhizoctonia root rots on pepper; Phytophthora crown rot, angular leaf spot, anthracnose, Cercospora leaf spot, powdery mildew, and downy mildew on squash and pumpkin; early blight, Septoria leaf spot, target spot, web blight, Fusarium wilt, and anthracnose fruit rot (ripe rot) on tomato; downy mildew on basil; Phytophthora crown rot on lavender; Rhizoctonia root rot on rosemary; and Pythium root rot on tarragon and thyme.
On ornamentals and turf, we have diagnosed anthracnose on clematis; Pythium and Rhizoctonia root rots, web blight, and leaf miner injury on chrysanthemum; bacterial soft rot on hosta; Pythium and Rhizoctonia root rots, and black root rot on milkweed; powdery mildew on zinnia; Volutella canker, Macrophoma leaf blight, and leafminer injury on boxwood; crapemyrtle aphid and sooty mold on crapemyrtle; Monochaetia leaf spot, rosette disease, and spider mite injury on rose; Cercospora leaf spot and bacterial leaf spot on cherry; thread blight on crabapple and filbert; Pestalotia and Phyllosticta needle blights on arborvitae; Phomopsis tip blight/canker on juniper and falsecypress; powdery mildew and Septoria leaf spot on dogwood; black spot on elm; Actinopelte leaf spot, anthracnose, iron chlorosis, and bacterial leaf scorch on oak; anthracnose on maple; anthracnose and Verticillium wilt on yellowwood; Rhizosphaera needlecast and spider mite injury on spruce; take-all, Pythium root dysfunction, Curvularia leaf spot, and black layer on bentgrass; brown patch, Curvularia leaf spot, and gray leaf spot on fescue; Pythium root dysfunction and summer patch on bluegrass.
By Julie Beale and Brenda Kennedy, Plant Disease Diagnosticians