Stubby root nematode causes stunting of plants. The symptoms described below may be an indication of a nematode problem, but are not diagnostic as they could result from other causes as well. Under moist conditions, secondary invaders such as bacteria, fungi, and onion maggots induce soft rot and decay of the bulbs. Root knot infestation can cause stunting, uneven stands of plants, and produces characteristic galls on roots. Galls induced by M.hapla are generally small and difficult to see, whereas galls produced by the other root knot species are larger.
Roots fed on by the stubby root nematode are extremely short with a yellow to brownish cast.
It is critical to know the nematode species present and their population densities to make management decisions. If a previous field or crop had problems caused by nematodes that are also listed as pests of onions or garlic, populations of these nematodes may be high enough to cause damage to seedlings. If nematode species have not previously been identified, take soil samples and send them to a diagnostic laboratory for identification. Divide the field into sampling blocks of between 5 and 20 acres each that are representative of cropping history, crop injury, or soil texture. Contact your farm advisor for more details about sampling, to help you find a laboratory for extracting and identifying nematodes, and for help in interpreting sample results.