FOR RELEASE THE WEEK OF AUG. 9, 1999:
Whiteflies flit around our tomato plants whenever we brush against the leaves. Do these insects cause enough damage to make spraying worthwhile?
Not usually, says Bob Stoltz, University of Idaho extension entomologist. "Unless you’ve got hordes of them and your tomato plants are really sticky, don’t worry about them," he says. "I’ve seen them in large numbers not doing any damage."
Whiteflies–which are actually closer to aphids than to flies–get their name from the mealy white wax that covers the wings and bodies of adults. They lay their eggs underneath plant leaves, where their feeding nymphs attach themselves until they develop wings.
The sap-sucking insects don’t generally spread plant diseases but they will "eat almost anything," Stoltz says. Inside greenhouses, where they flourish to menacing levels, they become significant economic pests. But outside, where they encounter plenty of natural enemies, they rarely build to high enough populations to warrant treatment.
Why do I have to add acid when I’m canning tomatoes? I thought tomatoes were acidic.
According to studies done in the 1980s, not all tomatoes are acidic enough to be safely canned with the water bath canning method. Unless their pH is below 4.6, foods must be preserved with a pressure canner, says Sandy McCurdy, University of Idaho extension food safety coordinator.
To make sure your tomato products are sufficiently acidic for water bath canning, add two tablespoons of bottled lemon or lime juice or one-half teaspoon of citric acid per quart of whole, crushed or juiced tomatoes. If you’re using powdered acid, make sure it’s citric–and not ascorbic–acid, McCurdy says. The ascorbic acid does not provide enough acidity.
Overripe tomatoes or those from killed vines should not be canned under any circumstances, she says. "Adding acids will not make them safe enough for home canning."
We’ve got a wasp nest under our eaves. How should we take it down?
Most of the Polistes wasps that hang round, "open-celled" or honeycombed nests from single stalks outside Idaho homes are not very aggressive, says Bob Stoltz, University of Idaho extension entomologist. "They eat a lot of caterpillars–and since most caterpillars are plant-eaters, the wasps are actually doing us some good," he says.
Still, if the wasps have built their nest where their comings and goings are interfering with yours, you’ll probably want to remove it. Buy a wasp- and hornet-killing aerosol spray. Very early in the morning or late at night, when the wasps are "home," shoot a 10-12 foot pencil stream of insecticide at the nest. Watch it for a day or so to make sure they’re dead, then knock down the nest. "If you knock it down while they’re active, you’ll get whacked," he warns.
According to Stoltz, it’s also a good idea to scrub the area where the wasps attached the nest. Use a bleach-based cleanser like Chlorox and "get rid of the scent so they don’t come back to the same spot next year."
I want to have grass under the trees in my yard, but it seems to be doing very poorly. How can I have a lush lawn?
Many grasses will become thin and spotty or die out completely if they don’t have at least 50 percent sunlight, says JoAnn Robbins, University of Idaho extension educator. Choose shade-tolerant grasses–such as fine fescue–for new plantings under trees or for renovating or overseeding as your trees grow larger. Mow those fine fescues at a high setting, since more light will be captured by more grass leaf area, and rake fallen leaves promptly. Professional thinning of thickly branched trees can also increase light penetration to the grass.
Robbins recommends fertilizing the grass under your trees more lightly and more often than the rest of your lawn. The idea is to fertilize the grass roots–not the tree roots.
Because tree roots also compete with grass roots for water, you’ll want to water more generously under your trees to encourage your grass roots to grow deeper. Every 10-14 days, supplement your regular watering with a deeper irrigation to make sure your tree gets enough moisture: the hotter the weather and the larger the tree, the more water you’ll need.
"The amount of water to keep a lawn healthy is not enough to grow a healthy tree," Robbins says.
Don’t forget to keep a grass-free area immediately around your tree trunk so that you don’t scar the bark with the lawnmower or weed-eater. That mechanical damage can weaken or even kill your tree.