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Common Pests and Problems for
April
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Frost is still possible this month. Do not uncover plants or plant tender plants too early. Little can be done to protect large trees and shrubs but you may be able to give some protection to small plants closer to the ground. Protecting Plants from Frost. Winter burn on broadleaf evergreen may also be noticeable at this time of year.
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Carpenter bees may be seen buzzing around decks and other wooden structures. Although males appear aggressive when defending their territory they can not sting. Females do not defend their nests but can sting if handled. Carpenter bees
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Carpenter Bees
Close-up of the exposed tunnels made by carpenter bees for their eggs. The grooves in the wood were made by woodpeckers drilling for the larvae.
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Apply crabgrass preventer by mid-April or by the time forsythia is blooming. If you decide to use a weed and feed product, do not use a fertilizer high in nitrogen. Crabgrass control
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Scout for and remove tent caterpillar webs. Treat now to help control lacebugs if they were a problem on azaleas or other plants last year.
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Eastern Tent Caterpillar
Eastern tent caterpillars (Lepidoptera) in web feeding on apple (Malus); note that the webs are in branch crotches
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Eastern Tent Caterpillar
Close-up of egg mass of eastern tent caterpillar (Lepidoptera) on flowering quince (Chaenomeles)
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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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Observe indoor seedlings closely for signs of damping off. Treat if necessary.
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Harden-off seedlings before planting in open ground to reduce or prevent transplant shock.
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Don’t plant tomatoes or other warm-season annuals such as petunias and vinca until the weather warms, usually in mid-to late May.
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Fluctuations in temperature can result in damage to flower buds of plants such as hydrangeas and magnolias.
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Remove mulch from roses in mid-April to limit damage from stem canker diseases.
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In late April or early May, inspect for and treat holly leafminers 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 cedar-apple and cedar-hawthorn galls on junipers before the orange spore-producing structures emerge from the galls.
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Scout for and control common spring insect pests such as aphids, spruce mites, and pine sawflies.
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Aphids - Outdoors
Aphids (Hemiptera) come in many colors; sometimes they blend into the background and are difficult to see; other times, they stand out, as do these red aphids
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Pine Sawflies
This pine sawfly larva (Hymenoptera) has eaten only the older needles of a Mugo pine (Pinus mugo) leaving new growth for next year's meal
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Weed whips can be deadly to plants, especially small trees when they girdle them by killing the bark at the base of the tree. Keep weed whips away from the base of trees and other plants.
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Resist the temptation to prune fruit trees including ornamental pears and oak trees now as they may be more subject to disease and insect damage at this time.
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Fireblight
Fireblight canker and twig dieback on crabapple (Malus)
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Cool-season grasses are best fertilized in fall. If you do apply fertilizer in spring, make sure it is low in nitrogen. Nitrogen applied in spring encourages excess growth, which is more susceptible to disease. Hold off until May to fertilize zoysia or other warm-season grasses.
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Be on the look out for sycamore anthracnose.
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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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© Missouri Botanical
Garden, 2001-2009
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