Answer: Either a severe leaf miner infestation or the weather, says Mike Orzolek, vegetable crops specialist with Pennsylvania State University at University Park. High temperatures and intense sun create a heavy water demand on plants. Unless that need is met through frequent watering, tender tissue in leafy crops such as spinach and beets can become scorched. In our area last season, especially in May, conditions were very hot and dry, notes Orzolek. To avoid leaf scorch, reduce the water loss any way you can. Mulch with a three inch deep layer of hay or straw and lay drip irrigation or soaker hoses in your beds of you don't have time to spray them with a hose, he adds. The other possible culprits leaf miners are the larvae of a small fly. They tunnel through leaf tissue, creating meandering gray white trails on the leaves of spinach, beets, chard and a great many other plants. If the infestation is sever, the tunnels can merge into white blotches, explains Orzolek. Adult leaf miner flies emergefrom the soil in early summer to lay clusters of small, white eggs on the underside of spinach and Swiss chard leaves. The eggs hatch in two to five days, and the larvae burrow into the leaf tissue. To control leaf miners, place a floating row cover over the greens in early June, before the adults lay their eggs, advises Orzolek. Handpick any damaged leaves to remove the larvae before they can reproduce.
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