Cause Pratylenchus penetrans, which lives in soil and causes plant decline by affecting the root system. Root-lesion nematodes are migratory endoparasites; part of the population is in soil and part in the roots most of the time. In peppermint, populations are relatively low through winter, peak in May, decline through late spring, then increase rapidly through the summer. Populations are highest generally just after harvest, then decline rapidly.
This nematode's most important role is to increase the incidence and severity of Verticillium wilt on both peppermint and Scotch spearmint. It also can reduce winter hardiness on both mint types.
Symptoms This nematode is the most frequent cause of open patches in a field with severely depressed, red-green plants with short, weak root systems. Roots and rhizomes have small reddish-brown lesions, which may blend together if the infestation is heavy.
Sampling Always include soil and roots in samples sent for nematode analysis if plants are present. Take samples any time if the numbers are interpreted in relation to nematode population dynamics. It is best to take samples in late summer to test for nematodes in fields that will be planted to mint so fumigation (if needed) can be done in fall.
- Use clean planting stock to prevent introducing the nematode.
- Preplant soil fumigation.
- Telone II at 9 to 18 gal/A depending on soil type. 5-day reentry. Restricted-use pesticide.
- Apply a nematicide in spring.
- Mocap EC at 4 quarts/A in 20-30 gal/A. Apply with ground equipment, broadcast, over the field. Do not apply by air or through any type of irrigation equipment. This product is to be soil incorporated to a depth of at least 2 to 4 inches, during or immediately following application by mechanical means, including by rotary tiller, rotary hoe, springtooth harrow, or by double discing, or by immediate application of 1 to 2 inches of overhead irrigation. Repeat irrigation before soil dries. Make only one application per growing season (either preplant or after last harvest of the growing season). Do not harvest within 225 days of application.
- Vydate L at 0.5 to 1 gal/A in enough water to cover. Apply as mint breaks winter dormancy with 0.5 to 1 inch of water within 7 days to move material into root zone. Do not apply within 21 days of harvest. 48-hr reentry. Restricted-use pesticide.
Reference Ingham, R.E., and Merrifield, K. 1996. Biology and management of nematodes in mint. IPPC Publication No. 996. Integrated Plant Protection Center, Oregon State University, Corvallis, OR. 39 p.