Nematode, Root-lesion

Root-lesion nematodes are invisible to the naked eye, but you'll see their damage aboveground: stunted growth, reduced vigor, off-color or wilting foliage, and poor fruiting on apple, blueberry, walnut, or other susceptible plants. If you dig up roots, you'll find small elongated brown lesions on fine feeder roots; heavy infections cause a witches' broom of damaged roots and loss of the larger feeder roots that should be absorbing water and nutrients. The problem is often spotty across a field, creating zones of clearly underperforming plants.

Pratylenchus penetrans (and related species) live in soil and migrate through roots throughout the growing season. Soil test results showing over 100-200 nematodes per 100g of soil can cause plant damage, especially if other stresses are present. The best management is preventive: rotate to new land if possible, use certified nematode-free nursery stock, and fallow or use non-host cover crops before replanting. For established plantings, control weeds thoroughly (many weeds host nematodes) and choose cover crops like tall fescue or yellow mustard, which has compounds toxic to nematodes. Soil testing before planting critical perennial crops like blueberries or raspberries can inform whether fumigation is needed.