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Common Pests and Problems for
May
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Hold off planting warm season vegetables, such as tomatoes, eggplants, vine crops; herbs, and warm-season annuals until the soil warms, usually in mid to late May.
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Continue to inspect for and treat for holly leaf miners as new leaves emerge.
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Holly Leafminer
Tunneling damage in holly (Ilex) leaf caused by holly leafminer, a fly maggot (Diptera)
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Holly Leafminer
Holly leafminer maggot (Diptera) between layers of leaf tissue on inkberry holly (Ilex glabra)
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Collect and dispose of bagworms as well as cedar-apple galls on junipers before the orange spore-producing structures emerge from the galls.
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Bagworms
Bagworms (Lepidoptera) pupate in very odd places.These probably moved to this fire hydrant from the juniper nearby.
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Cedar-Apple Rust
When orange gelantized telia appear on the cedar host (Juniperus virginiana), basidiospores from it are infecting the apple host (Malus) of cedar-apple rust
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Apply protective sprays on apples and hawthorns for rust disease if warranted.
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Do not prune apples and other plants susceptible to fireblight at this time of year as you can spread the disease. This also applies to black knot, which affects plums and other member in the Prunus genus.
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Fireblight
Fireblight canker and twig dieback on crabapple (Malus)
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Check pines and junipers for signs of tip blight. Cankerworms may be observed at this time of year but they usually do little damage and do not warrant control.
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Monitor pines for sawfly damage. Also check for crawlers of euonymus and pine scales.
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Pine Sawflies
European pine sawfly (Hymenoptera) rearing up in characteristic defensive posture on pine (Pinus)
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Treat for borers if found in dogwood, ash, lilac, apple, and peaches.
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Lilac Borer and Ash Borer
Sap flow from a borer hole (Lepidoptera) in trunk of a summit ash (Fraxinus pennsylvanica 'Summit')
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Scout for slugs, which chew holes in leaves and cutworms, which can cutoff young plants at ground level.
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Watch for sod webworms towards the end of the month.
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Treat broadleaf lawn weeds if warranted while they are still actively growing. Weeds are more difficult to kill with herbicides as their growth slows when weather warms.
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Monitor azaleas for early signs of lacebug damage.
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Lacebugs
White flecking on upper leaf surface on azalea (Rhododendron) caused by feeding of lace bugs (Hemiptera); heavy infestation
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Lacebugs
Heavy infestation of lace bugs (Hemiptera) on underside of azalea (Rhododendron) leaves; silvery white adults, dark nymphs, dark spots of excrement
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Scout for eastern tent caterpillars and destroy webs if found.
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If boxwood leaves are infested with leaf miners, some control can be obtained by pruning the plants back and disposing of the leaves before the adults hatch in late May.
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Boxwood Leafminer
Damage to boxwood (Buxus) caused by boxwood leafminer (Diptera), a fly maggot; later stage
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Boxwood Leafminer
Close-up of boxwood leafminer (Diptera), a fly maggot, exposed in the tunnel it has eaten between the layers of a boxwood (Buxus) leaf
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Other problems to be on the lookout for are anthracnose of sycamore and the taxus mealybug.
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Indoor plants moved outside for the summer are very susceptible to sunburn. Acclimate plants gradually to outdoor conditions to avoid setting them back.
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Be on the lookout for asparagus beetles.
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Do not harvest and eat rhubarb that has been damaged by a late frost.
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Apply a preventative insecticide spray to the trunks of peach trees and other stone fruits in the first half of the month to control peachtree borers. Apply again in August.
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© Missouri Botanical
Garden, 2001-2009
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