While nematodes may be too small to see, they’re causing problems too large to ignore. Losses are staggering. The Society of Nematologists estimates that plant parasitic nematodes cause more than $3 billion worth of crop losses annually.
- Reniform nematodes are the most destructive type in the south in cotton and can cause yield losses of upward of 50% in severe cases, and currently account for $130M in annual losses to the U.S. cotton industry.
- Columbia lance nematodes commonly generate losses from 10% to 25% per field in cotton and soybeans, but can exceed 50% in sandier fields under drought stress.
- Root-knot nematodes can cause losses in many crops, including corn, soybean and cotton.
- Sting nematodes can be extremely damaging to cotton at low population densities, and can lead to complete crop destruction at higher densities.
In 2014, cotton yield losses due to nematodes were estimated to be 870,000 bales.
(per 100 cc soil)
||Coarse or Sandy
||50 to 500
||Throughout the Cotton Belt. Root galling, stunting, wilting and premature death with Fusarium wilt pathogen interactions. Spotty within a field.
||Moderate; Severe with Limited Geographical Distribution
||Sandy Loam, Sandy
||250 to 500
||Primarily in the coastal plains of NC, SC, and GA. Seen in LA and AL. Taproot stunting, increased secondary branching, above ground stunting and mild chlorosis.
worse with coarse soils
|1,000 to 5,000
||NC to West TX. Stunting, delayed maturity and reduced yields. Potassium difficiency in severe cases. Can interact with soil diseases such as Rhizoctonia, Pythium and Thielaviopsis.
||Sandy Loam, Sandy
||10 to 25
||Sting can be found in most southeastern states, but is restricted primarily to old river bottoms or other very sandy areas. Can be extremely damaging to cotton. Generally restricted to small areas of a field.
Perhaps the most troubling aspect of the nematode issue is that the symptoms of nematode attacks either can’t be seen or are often credited to other problems. Because the symptoms are common to a number of crop stresses, it is sometimes difficult to distinguish nematode damage from insect or herbicide injury, nutritional deficiencies or soil problems. All soil types – not just sandy soils – can have significant infestations of plant-parasitic nematodes.
Symptoms in cotton can include:
- Stunted plants and roots
- Leaf yellowing
- Wilting of the plant
- Plant stress
The question should never be whether to test, but when to test.
Populations grow throughout the season. University nematologists generally recommend sampling for cotton nematodes in the summer or late fall.
Soil sampling is the best way to determine which species of nematodes are in your fields and at what levels. Check with your state’s land-grant university or Extension agent to find out where to send samples.
For more tips on nematode testing, download the Nematode Sampling Guidelines.
Nematodes are parasitic, and their life cycle is fairly common across types. Although nematodes progress through the stages of egg, juveniles, and adult, it is the juvenile stages that represent a threat. Here’s how they cause damage to your plants.
- Juvenile nematodes travel toward identifiable food sources – the roots and the exudates. When they encounter a root system, the juveniles of some nematodes penetrate the root and move into the cell in search of nutrients.
- In some species of nematodes, females swell so large they break through the root surface and become visible to the naked eye. Impregnated by male nematodes, they fill with eggs and eventually die, their body cavities forming cysts that incubate hundreds of nematode eggs.
- Other nematodes feed from outside the root surface using needle-like structures, or stylets, to pierce the root, creating an opening that allows them to remove nutrients. Most nematode species complete several life cycles during a plant’s life, while a few species take a year to finish the cycle.
Some nematode species can produce six generations in a single year.
Image courtesy of The American Phytopathological Society