September 1996 - Indiana Yard and Garden - Purdue Consumer Horticulture

September 1996

Q: For the last three years, my husband and I have had a problem with our zucchini plants. After one or two pickings, the plants are plagued with a gray-brown bug that looks like a stink bug. Soon, the plant dies. We have put Sevin on the plant as soon as we see the insects, but the plant still dies. We destroy the plant correctly and put diazinon in the ground to prevent further infestation but still, even after planting the seeds in various places in our garden, the plant seems to get the insects. Do you have any ideas as to what could be causing this besides the worm or the eggs on the leaves that we spray? What can we do to get healthy plants that produce throughout the whole growing season?

The strange part is there are cucumbers nearby, and they are not affected, nor the butternut squash, also nearby. We rotate crops every year. Any suggestions? – Irene Chidester, DeMotte, Ind.

A: One likely possibility is the squash vine borer. All cucurbits are susceptible to its attack, but squash (especially summer) and pumpkins are prime targets. For several concurrent years I lost all my zucchini and cringed when others joked about their surplus.

Eggs are laid on the vines, and young larvae immediately bore into the plants. The white grub-like caterpillar feeds inside, where it is protected from some insecticidal sprays. Damage often is first noticed by the sudden wilting of an otherwise healthy vine or entire plant.

When a vine is found wilted, the stem should be split at the entrance hole, and the larvae removed. If, however, the injured plant part is covered with soil, new roots will often form, and the plant will survive.

Another possibility is the squash bug. It doesn’t usually kill a vine so quickly, but the adult resembles your description more than the squash vine borer. It’s certainly possible you have both! The nymphs and adults of the squash bug suck sap from leaves and unripe fruit, causing plants to wilt and die and fruit to collapse. For both pests, destroying crop residue will reduce the problems you will have next year. The only other in-season alternative is to put on protective sprays of carbaryl (sold as Sevin) beginning when the plants start to run. It is crucial to reapply as directed on the label.

Q: Bonnie Day of LaGrange, Ind., and Ruby Stringer of Greencastle, Ind., both wrote inquiring about trumpet plant, or hummingbird vine. Their plants are 2 and 3 years old. The foliage grows nicely, but they refuse to bloom. Bonnie gives hers plant food.

A: You are probably both referring to Campsis radicans, sometimes called trumpet creeper for its large, trumpet-shaped, orange flowers that are very attractive to hummingbirds. Michael Dirr, author of “The Manual of Woody Landscape Plants,” writes, “If you cannot grow this, give up on gardening.” But neither of you are having trouble getting it to grow – just in coaxing it to bloom!

Several causes can keep plants from blooming, but in this case it’s probably too much nitrogen. Excess nitrogen encourages foliar growth at the expense of flowers. Trumpet creeper blooms profusely along country roads where it receives no care at all, so it shouldn’t require fertilizer. Regular fertilizing of the surrounding lawn can also boost nitrogen to high levels.

If your vines are growing in a shady location, move them or prune overhanging branches so they receive more sunlight. At least a half day of sunshine will promote blooming. Finally, Dirr recommends pruning back to several buds in spring.

Q: I have two ‘Fairy’ rose bushes growing 4 feet apart, seemingly healthy. Each year it’s the same story – one has lots of roses, but the many buds on the other can’t open. Should I put it out of its misery? – Ruth King, Huntington, Ind.

A: Roses are host to a number of insects and diseases, so I can’t give you a definitive diagnosis, but here are some possibilities: Thrips are small (one-twentieth of an inch) insects that attack buds in their early stages. The buds become deformed and fail to open properly. Control them with two or three spring sprays of insecticidal soap, carbaryl (Sevin), malathion or diazinon. Remove and destroy all infested blooms and buds.

Botrytis blight causes the buds to turn brown and decay instead of opening. Buds may also have a gray mold. Avoid problems with good garden sanitation. Keep dead leaves and flowers picked up so the fungus will not have a chance to produce quantities of spores. Keep the foliage as dry as possible by watering at soil level instead of overhead. Fungicides also can help. Spray with chlorothalonil (daconil) or captan every 10 to 14 days as long as the mold is visible.

Bacterial leaf spot also can keep plants from blooming. Spots are usually dark-colored, and are sometimes accompanied by rotting and oozing from infected areas. Again, pick off and destroy infected leaves, and clean up all plant debris.

To pinpoint the problem, bring a sample to your county office of the Purdue University Cooperative Extension Service.

Readers: The sweet potato saga continues! I received the following letters from readers suggesting various culprits.

Q: We like eating sweet potatoes, and we plant two or three acres. We live on a farm with good soil in the famous watermelon district of Knox County.

One early fall day about 15 years ago, we were digging a few hills of sweet potatoes when we found a nice large sweet potato that was almost all eaten. Inside this potato was a 10- to 12-inch salamander doubled over. Our grandson wanted to take it home. Because of the way various sweet potatoes had signs of eating on them, I’ve often wondered if there was a small colony of salamanders with good appetites nearby.

Down through the years, three more salamanders have been found and given to our grandson. They are still living. Now I wonder how many other critters enjoy a sweet potato patch. – Dorothy Williams, Vincennes, Ind.

A: It’s an interesting theory, but salamanders eat insects, leeches, worms, frog eggs, small crustaceans, and other protein-packed items. They aren’t big on vegetables. They may have been attracted to insects that were eating your sweet potatoes, which would explain why one was happily reclining in your tuber. Canned dog food is a good meal for captive salamanders. Your grandson may have already figured that out.

Q: I believe your column stated that moles don’t eat sweet potatoes. Maybe not, but here is my story. It was probably three years ago that I went to dig mine and was finding only shells – the inside of the potato was gone. As I went down the row, I became more frustrated and wondered what was eating them. Then, one time when the fork came up, I had run it right through a mole, so I assumed that was the thief. I guess one could call that circumstantial evidence, not proof. I have not grown sweet potatoes since, but I’m trying again this year. – Virginia Spelbring, Poland, Ind.

A: You hit the nail on the head (and the mole) when you said it’s circumstantial evidence. Your mole and the salamanders above are both probably interested in the sweet potato patch because of loose, friable soil, regular moisture, and an abundance of earthworms and other insects. There is no scientific proof to date of moles eating many sweet potatoes. They are largely carnivorous, but the following percentages reflect the portion of their diet that is vegetable matter: 1.9 percent grass seed, 1.5 percent wheat seed, 1.1 percent sorghum seed, and 1.4 percent unidentified material. Perhaps that 1.4 percent unidentified material is the amount of sweet potato stuck to the insects feeding on your sweet potatoes that the moles are eating!

Another possibility is mice using the mole tunnels to feed upon the sweet potatoes. You may have stabbed the mole that was creating a nice road system to an easy meal for a mouse.

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