TEMPERATURE DEPENDENCE OF DAMAGE THRESHOLDS:

• CYST - (50F,10C)
  • COASTAL REGIONS (2-3 EGGS/GRAM IN COOL SOILS)
  • IMPERIAL VALLEY (1 EGG/GRAM)
• LESION - (59F, 15C)
• STEM & BULB - (59F, 15C)

Damage thresholds are often thought of as absolute numbers. For nematodes, at least, the temperature at the time of planting can be a major factor in determining rather or not damage will occur. If the temperature at the time of planting is below the activity or infectivity threshold (some examples are given in the table above) of the particular nematode of interest, less damage will be experienced than if temperatures are warmer.

The damage threshold for sugarbeet cyst nematode is higher in the coastal regions of California where soils are cooler than in the Imperial Valley of Southern California.

It is common practice to recommend that sugarbeets be planted when soils are cooler and less damage will be experienced from sugarbeet cyst nematode. This recommendation, however, is often in conflict with recommendations made by entomologists who recommend delaying planting until June to avoid aphid transmitted virus yellows disease.

P. thornei is known to cause serious problems on wheat in Mexico. It is commonly found in fields in Northern California but is not considered a problem on wheat. This is probably due to the fact that wheat is grown in the winter when soil temperatures are below the activity threshold of the nematode.

NEXT

UNIT INDEX

MAIN INDEX