Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
May Garden Activities
Protect honeybees. Use caution when applying insecticides to flowering plants.
- Mow turfgrasses frequently at 3 to 3 1/2 inches. Don't remove more than 1/3 of the topgrowth at each mowing.
- Watch for bluegrass billbug adults. Treat when adults average 1 per square foot.
- Warm moist spring weather often results in fungal slime molds & mushrooms in home lawns. No chemical treatment is recommended. Pick and throw away mushrooms before mowing to reduce the number of spores. But the mushrooms will continue to pop up until the decaying material they feed on is gone, such as buried wood, decaying tree roots, or thatch. Slime molds sometimes look like dog vomit (hence the name dog vomit fungi) and can come in many bright colors, while others appear as grayish mass on turf leaf blades. Symptoms of leaf blade smile molds may be seen as irregular patches of discolored turf ranging in size from several inches to several feet in diameter. Some slime molds feed on decaying material and are often found in mulched ornamental beds, while others use turf leaf blades strictly as a structure to grow on.
- May 30 to July 30, apply preventive summer patch control on lawns with a history of this disease.
- Plant sweet potato slips after all danger of a frost has passed.
- Fertilize established asparagus plantings after the final harvest.
- Continue streptomycin applications for fireblight control on on apples, crabapples and pears.
- Continue fungicide applications on apples, crabapples and pear for cedar-apple rust and apple scab.
- Control cherry leaf spot, beginning at petal fall, with a fungicide application every 10-14 days as fruits mature. Four or more applications may be necessary for control. Some chemicals cannot be used on trees grown for fruit production/comsumption.
- Early May make a second fungicide cover spray on sycamores for anthracnose.
- In early May watch for first generation oystershell scale crawlers to appear now and the second generation in August; treat with horticultural oil, insecticidal soap or acephate if necessary.
- Watch for ash leafcurl aphid.
- May 10, Spray the trunk and large branches of lilac and ash with permethrin to control the common lilac/ash borer. Repeat in 3 weeks.
- Late May, if fungicide cover sprays were not applied to sycamore for control of anthracnose, this is the time for a fungicide trunk injection.
- May 31, Second application to the trunk and large branches of lilac and ash with permethrin to control the common lilac/ash borer.
- Spray trunk and branches of birch trees with permethrin in late May to control bronze birch borer. Repeat in three weeks. Alternative- make a soil drench application of imidaclopirid.
- Bright orange lesions on leaves of ash trees is a fungal infection called Ash Rust. Heavily infected leaves may be shed from the tree, but overall the disease will not serious affect the health of mature trees. Chemical control is not recommended.
- Second application of copper fungicide to long-needle pines, such as Austrian and Ponderosa, for Sphaeropsis tip blight.
- Mid May apply first application of copper fungicide to pines for Dothistroma needle blight; repeat in late June.
- On spruce control Rhizosphaera needlecast and Siroccocus shoot blight with the application of a fungicide (chlorothalonil) when shoots are 1/2-2 inches in length; repeat application 3-4 weeks later.
- Watch for pine tip moth caterpillars. Affected shoots turn brown and dieback, with evidence of tunneling in the center of the shoot. Affected branches and plants may be unattractive but little serious damage is done. If necessary, make an insecticide application the 3rd week of May, 2nd week of June and 3rd week of July.
- From late May to early June, watch for hatching of bagworms on juniper, spruce, fir and other deciduous plants. Make one application of Bacillus thurengiensis (Dipel, Thuricide) or other insecticide for control. Thoroughly cover the entire tree.
- First fungicide cover spray on raspberries for anthracnose. Make a second application in 10 days.
- At the first sign of Botrytis infection of peony remove infected leaves and stalks. Infected young stalks wilt, young buds turn black and dry, later buds turn brown and become covered with a brown or gray mass of fungal spores. Plan to cut all stalks to the ground in fall and eliminate as much disease pressure as possible.
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