The Corn Cyst Nematode
Damage to Corn. Damage to corn by corn cyst nematodes
may be considerable, as small
numbers of the nematode have been found to cause
serious damage. Losses varying
from 5.5% to 39.2% have been noted, depending on
Biology. Adult females are pear
or lemon-shaped and pearly-white, turning light to dark brown as the cyst
matures. Eggs are generally retained in the cyst until they hatch.
Temperature plays an important role in the biology of H.
zeae. The life cycle is short, taking only 15-17 days if temperatures
are optimally warm (about 27-39 C). It has been speculated that the nematode
may complete six to seven generations during one crop season. Under conditions
in Maryland, cysts with infective juveniles apparently only persist in
fallow soil for about two years.
zeae was first described from India where it is widely distributed.
It has also been reported from Pakistan, the Nile Valley, Egypt, and Maryland
in the USA In Maryland, it is found primarily in heavy silty-clay soils.
A cold, wet period in spring facilitates hatching of the nematode, and
invasion of the root.
Symptoms. Plants affected by corn cyst
nematode are stunted, pale in color, with narrow leaves. Stunting
frequently occurs in irregular patches, and development of tassels may
be noticeably delayed. As with other cyst nematodes, the presence
of cysts on the root surface is the most important characteristic used
in the identificaion of H. zeae.
Damage to other crops. Other economic hosts include
millet, oat, rice, sorghum, sugar cane, and wheat. Several grass weed hosts
have been identified in India and the USA
Control. After cyst nematodes have infested
a field, it is practically impossible to eliminate them. Crop rotation
every 4-5 years with non-hosts helps maintain populations below threshold
levels. Susceptibility to Heterodera zeae varies widely
among corn cultivars, providing the possibility of some resistance