Published on January 22, 2008
Symptoms of Nematode Damage to Plants: Symptoms of Nematode Damage to Plants The above-ground symptoms of most soil nematodes are non-specific. They often mimic damage caused by fungi, bacteria, lightning, root-feeding insects, or fertilizer problems. This symptom (chlorosis) on peanut could be attributed to nitrogen deficiency, lightning strike, or fungal pathogen. In fact it is caused by a root-knot nematode feeding on the roots. Irregular spots of dieback or dead plants can have numerous causes. Root systems and soil samples need to be analyzed. This cotton problem was caused by a Fusarium-root-knot nema complex (cotton stunt). Above-ground Symptoms: Suggestive But Not Conclusive I: Above-ground Symptoms: Suggestive But Not Conclusive I Both banana (left) and boxwood (right) have a number of foliar problems. In both of these cases, roots and soil samples must be examined, at least until enough samples are seen so the diagnostician is reasonably sure of the problem. Burrowing nematode on banana is a devastating disease in the tropics, causing bananas to topple as the bunches are growing. Lesion nematode is one of the few major disease problems on boxwood, and has accounted for significant losses of heirloom boxwoods in historic neighborhoods. Above-ground Symptoms: Suggestive But Not Conclusive II: Dieback is a common symptom of pathogen infection in trees. Above: spreading decline of citrus caused by the burrowing nematode. Right: coconut wilt caused by the red-ring nematode. Both of these nematodes are serious threats to citrus and coconut production. Above-ground Symptoms: Suggestive But Not Conclusive II Above-ground Symptoms: Suggestive But Not Conclusive III: Above-ground Symptoms: Suggestive But Not Conclusive III Stunted growth in a field can be due to lots of different problems, such as fertilizer skip. Feeding of nematodes on roots can cause the same symptoms. This is sting nematode on cabbage in a nematicide trial. Roughly circular or irregular, radiating patches of dead and dying lawns or sports turf could be fungi or insects, or could be nematodes. Examination of soil is necessary. This symptom is on a golf green in west Tennessee and is caused by sting nematode. Root Symptoms: Root Symptoms Root galls; Stubby root; Root lesions (necrosis) Root pruning; Root bushiness. Root Symptoms: Galls caused by Root-Knot Nematodes: Root Symptoms: Galls caused by Root-Knot Nematodes The diagnostic symptom of RKN infection is galling of the root system. No other pathogens have precisely this effect. Galling occurs due to hypertrophy of the giant cells in the vascular tissue (food source) and hyperplasia of the cortex. Heavy infection results in the coalescence of many individual galls into large, lumpy swellings. tomato tomato abelia Root Symptoms: Effects of Plant Species on Galling: Root Symptoms: Effects of Plant Species on Galling Gall morphology can differ among plants. These root systems are infected with M. hapla : L-R: canary creeper, onion, soybean. Root Symptoms: Destruction of Feeder Roots: Root Symptoms: Destruction of Feeder Roots Root necrosis is a common symptom of nematode feeding. Damage to and death of the fine feeder roots leads to wilting, chlorosis, and dieback of the above-ground portion of the plant. These symptoms are particularly characteristic of lesion and sting nematodes. On the left, lesion nematode feeding causes root pruning and necrosis on potato. On the right, massive attack of sting nematode on soybean has caused extensive root death and blunting of growing points (“stubby root”). Symptoms on Storage Roots : Symptoms on Storage Roots Nearly all vegetables are good hosts of nematodes, especially root-knot nematodes. Some resistance is known for RKN on tomato, but most other veggies have no known resistance. Infected plants are still edible and the nemas pose no hazard to human health; however, deformities make a root crop unappealing and unsaleable. Symptoms on Tubers and Rhizomes: Symptoms on Tubers and Rhizomes Infected potatoes have warts. In cross-section, each reddish dot is a the location of a female nematode. A thin section illuminated with transmitted light shows the location of each female (f). The cleared areas are regions depleted of starch, brought about by the demand of the giant cells for nutrition. Infection of yam by the yam spiral nematode creates avenues of entry for rot fungi that can ruin an entire stored crop. healthy infected Potato Yam Symptoms on Peanut: Symptoms on Peanut RKN is a serious threat to peanut crops worldwide. In a heavily infested field, root and pod infection greatly reduces quality and quantity of yield. Damaged pods have necrotic areas, probably due to secondary pathogens,and are reduced in size. In the picture, each group has 16 pods. Group A was grown in the presence of RKN, Group B was free of nemas. Highest prices are paid for peanuts suitable for human consumption; unsuitable pods are used for animal feed and fetch minimal prices. Symptoms on Onion: Symptoms on Onion This photograph is from a classic study done decades ago with lesion nematode on onion. Nematodes were added to plots at rates of 0-18,000 nematodes/kilogram of soil. This photo represents the harvest, with the same number of onions in each bag. This experiment demonstrated that this lesion nematode was an important constraint on onion production. Nematodes That Attack Above-ground Plant Parts: Nematodes That Attack Above-ground Plant Parts A few groups of plant-parasitic nematodes can feed in the above-ground parts of plants. The white-tip nematode causes severe damage to rice production, and the stem nematode is a major constraint on alfalfa production. Many herbaceous ornamentals are disfigured by leaf and bud nematodes.