Controlling crab spider populations around your home

Aloha, Nick. Thank you for all the good info on your website.

Aloha, Nick. Thank you for all the good info on your website.

I live in Kalapana in a forested area. I have been bitten by crab spiders inhabiting my greenhouse. I have been destroying their webs, but nearly every day I am exposed to them. I frequently feel webs in my hair and then they bite me, causing a very itchy rash on my scalp, neck and shoulders.

Today I ordered a gallon of Neen oil and I plan on spraying the greenhouse when it arrives. Could you please tell me how I can mix it to be effective? Thank you, D.

First let me say that you can find an article about crab spiders on www.gardenguyhawaii.com. It’s under “Mites and Spiders.”

Horticultural oils, including neem oil, and soap solutions will kill the spiders when they are sprayed. However, these products will only kill what they contact; there is no residual. This, of course, can be good or bad depending on how you look at it.

You may not want to use other types of insecticides, but a common household spray with the active ingredient bifenthrin, a synthetic pyrethroid, is a material sold in many home and garden stores. Not only will it kill by contact, but also leaves a residue for several weeks which will have an effect on any new spiders that come in. You may only have to spray the greenhouse once every one to four months to get good control.

FUZZY BUGS ON THE ROOTS

There are species of both aphids and mealybugs that attack the roots and the crown line of plants. Oftentimes when potted plants are pulled out of the pot, whitish fuzzy bugs in the soil or on the roots can be seen. A fairly common attacker is the pineapple mealybug. Adult females are described as plump and convex in body shape and pinkish in body color.

The pineapple mealybug is primarily a pest of pineapple and other bromeliads, but it also attacks banana, citrus, cotton, coffee and hibiscus. It is found wherever pineapple is grown and is present on all of the major Hawaiian Islands. Plants rarely die from a mealybug infestation.

Control of this mealybug centers on the control of ants which provide the mealybugs shelter and protection from natural enemies. With the ants controlled, mealybug populations usually remain small.

In infested areas of the garden, after the crop is removed, the soil should be turned over and all crop residue and grassy weeds removed. Host plants of this pest (listed above) should not be grown in this bed for at least a year.

If you’re going to be planting a lawn this spring, I recommend reading the University of Hawaii College of Tropical Agriculture and Human Resources publication, “Adaptation of Turfgrasses in Hawaii.” Planting the wrong grass for what you want can be costly in labor, time and expense. CTAHR’s publication looks at over a dozen turfgrass species and rates them for numerous characteristics like their tolerance to shade, wear, drought, their nitrogen requirement, leaf texture and whether they are high or low maintenance.

Another publication, “Common Lawn Grasses for Hawaii,” lists the desirable and undesirable characteristics of more than 15 of Hawaii’s grasses.

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There is still time to sign up for Saturday’s vegetable gardening class. It will be from 10 a.m.-12;30 p.m. at the University of Hawaii at Hilo, UCB 118. Topics include soil preparation, fertilization, transplanting versus direct seeding, common diseases and insect pests that attack vegetable plants and which vegetable to plant. Call 974-7664 or register online at http://hilo.hawaii.edu/academics/ccecs/registration/ There is a fee.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at askthegardenguy@earthlink.net.