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Diagnostic Tidbits (Week of July 23) - Jul 30, 2012

by UW Extension Plant Health Clinic Team

Listed below are this week’s plant diagnostic and growing tips from the Plant Health Clinic team.

Spider Mites and its damage

Spider mites are pests that feed by sucking sap from plants.  Typical damage is small yellowish spots on the plants leaves.  These mites go through four to six generations per year and populations can explode under warm, dry conditions.  As the mite population swells the leaves they are feeding on will turn yellow, then brown and die.  Spider mites are hard to see with the naked eye so inspecting leaves (top and bottom) with a magnifying glass may be necessary.  Hosing off the underside of your plants leaves will dislodge many of the spider mites.  Insecticides don’t work well on spider mites; in fact it may kill natural predators that would eat the mites.

Why are my cucumbers hollow in the middle? I've been feeding them weekly and watering.

If the plant has beautiful, large green leaves and seems be extremely healthy, you are over fertilizing. The fruits are growing too fast to fully develop. Cut back on the feeding to once a month but continue to water on a regular basis. Water using a soaker hose in the morning for best results or be careful to gently water at the base of the plants in the morning. This will allow the leaves to dry nicely before the day heats up. Try not to wet the leaves or splash up the soil as this can create the perfect conditions for molds and fungal infections to develop.

Chinch Bugs in Lawns

Chinch bugs are insect pests of turfgrass that can cause serious injury to Wisconsin lawns.  Damage is usually apparent from late summer to early fall but can appear anytime from late June until first frost.  Chinch bugs feed by inserting their beak-like mouthparts into the plant and sucking out juices.  During feeding the bug injects a toxic saliva into the plant.  The toxin causes plants to continue to wilt and yellow even after the chinch bugs have been controlled.  This will give lawns a droughty appearance even though sufficient moisture may be present.  Chinch bugs prefer hot dry areas; damage may be noticed first on slopes and in open sunny areas, such as along sidewalks and driveways. To determine if your lawn has chinch bugs take a coffee can and remove the top and bottom.  Twist the can through the turf into the upper soil layer.  Fill the can with water and agitate the grass with your hand.  Any chinch bugs will float to the surface.  Treatment may be necessary if there are 2-3 chinch bugs per test area.  Bifenthrin, carbaryl and cyfluthrin are recommended for home use; use in accordance with the label.  Only apply chinch bug insecticides as necessary; do not apply them on a routine preventative basis.  Controlling weeds, fertilizing properly and irrigating during hot dry periods will help your lawn tolerate small infestations of chinch bugs.

What causes the squash vine to wilt in day?

Damage caused by squash vine borer larvae often goes undetected until infested plants wilt and die in late July and August.  The first symptom of feeding damage is when plants wilt midday.  This wilting is caused by larvae as they tunnel through vines and destroy the tissue that transports water.  Wilt symptoms may be confused with those caused by bacterial wilt.  To distinguish between squash vine borer injury and these diseases, look for entrance holes near the base of wilting vines.  If frass (i.e., feces) is present near the entrance holes, split the stem lengthwise to confirm the presence of larvae.  Fields that have been damaged in the past are likely to be damaged again. Two to three insecticide treatments, five to seven days apart during the three week egg-laying period around 1000 degree day 50 will control most of the larval borers before they burrow into vines and become protected by vine tissue.  Treat plants with runners that are less than two feet long is particularly important.  For a list of pesticides that will control squash vine borers, refer to UWEX publication A3422 “Commercial Vegetable Production in Wisconsin”.  Floating row covers may also be used during the flight period in June. See this article for control specifics.


Should I mulch my plants?

Mulching in this heat is a great idea!  Mulching helps retain moisture in the soil and reduce weed competition.  Organic mulches such as grass clippings, straw or compost are excellent choices for your vegetable gardens.  Hardwood mulch would be best for your trees and shrubs.  Suitable mulches for flower beds would be hardwood mulch, compost, cocoa bean or cottonseed hulls.  Mulch to a depth of two to three inches.  Over mulching can actually stop the rain from getting into the soil.  The mulch can act as a sponge and absorb most of the moisture.

How do I remove the suckers from around my trees?

Suckers are the growth of branches from the base of trees and single stemmed shrubs.  This is more likely to happen when trees are under stress; such as drought, severe pruning and limb loss. Trees grafted onto a different rootstock (Ex. apples) are very prone to suckers.

Remove suckers using a sharp, clean pair of pruning shears. Cleanly cut the plant sucker as close to the tree as possible, but leave the collar (where the tree sucker meets the tree) to help speed the wound recovery.  If you have lots of trees with many small sprouts, they can be mowed down with a lawn mower.

If you’re bugged by garden pests or would like some free gardening advice, get your horticultural questions answered by the UW Extension Plant Health Clinic team located in the lower level of the Visitor Center and at the Brown County UW Extension office. Check out our website for Plant Health Clinic hours and contact information.

UW Extension Plant Clinic Staff members – Vijai Pandian, John Hermanson, Lynn Clark, Dan Mitchel, Sue Roulette, Vicki Warden, Ritalyn Arps and Ryan Sievert


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