Potentially the two worst cucurbit pests

Bill Kerr takes a look at how to identify and treat Eelworm and pumpkin fly damage in cucurbits
Issue date: 2-9 January 2009

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The world’s worst pest, eelworm, is also a problem for cucurbits. If the crop starts to grow unevenly and the more stunted plants wilt despite sufficient moisture, the likely culprit will be root knot eelworm (Meloidogyne Sp.) Eelworm, or nematodes, are easily seen as round swellings on the roots. They affect the uptake of water and nutrients and can render a crop totally unproductive. Fortunately, today there are systemic products which can be applied to the crop to suppress them enough to restore normal growth, although yield will still be lower.

Always inspect the roots of crops reaching the end of their lifecycle for this pest. Look in the areas where the crop looks less vigorous. If eelworm is detected, the rows should at least be fumigated before planting cucurbits. The various preplant treatments may have withholding periods after application before the crop can be planted. If an eelworm-susceptible crop was planted before the cucurbits, we often see a peculiar pattern developing if the cucurbit rows cross the previous ones. We can often identify where the previous rows were just by the higher eelworm population in these areas.

A notorious cucurbit pest is pumpkin fly. A high population of these brownish flies, when fruit has just stared forming, can destroy a crop. They lay their eggs in the fruit by inserting their ovipositor through the skin into the flesh. The elongated eggs are easily seen when cutting through the sting lesions, which are easy to detect on the fruit.
Young fruit are completely destroyed and when older fruit are stung, the eggs will develop in a pocket in the fruit. The fruit may still be marketable, but second-grade.
The yellow maggots leave the fruit when mature and pupate in the soil. They can curl up and spring a short distance from the fruit.

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Pumpkin flies originated in low populations that can overwinter in cold areas. Higher populations do most of the damage later in the season. Only a few fruit are initially affected, which usually go unnoticed. If these are controlled, one can usually get far into the season without further damage. Lebaycid is a systemic product which works rather well and Pyrethroids can also be effective in controlling the flies on contact. Baits can also be used by spraying coarse droplets on the foliage, in conjunction with Lebaycid if necessary. – Bill Kerr ((016) 366 0616 or e-mail [email protected]).     |fw