In the summer of 1993, a previously unknown disease of corn was detected in
Colorado, Kansas, and Texas, and in Gooding, Jerome, and Twin Falls counties in
Idaho. The disease is called the High Plains Disease (HPD) or High Plains "Virus"
Disease, based on its initial detection in the central United States. In Idaho, this
disease affected about 750 acres of sweet corn, with yield losses exceeding 50
percent in several corn fields. Two fields under center pivot irrigation, totaling 195
acres, were abandoned because of the disease. In 1994, HPD was confirmed in
several sweet corn fields in southwestern Idaho, where most of the United States’
supply of sweet corn is produced.
Although HPD has affected only sweet corn in Idaho, it has affected sweet and/or
field (dent) corn in other states, including Utah, which reported the disease in 1994.
HPD is spread by the wheat curl mite (Aceria tosichella), but its cause has yet to be
identified.
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Primary symptoms of the disease include stunting, chlorosis (yellowing), and a
mosaic pattern on leaves. The severity of these symptoms depends on variety,
stage of growth when infection occurs, and sometimes other factors.
Stunting and yellowing are very apparent when young
plants are infected. The mosaic pattern, which
appears as little spots or short streaks scattered across a green surface or as
green spots or streaks on a yellow surface, may be seen on the plant’s leaves. In
younger leaves, this pattern will appear near the whorl.
In advanced stages of HPD, chlorotic stripes a inch
wide or more may form and run parallel to the leaf veins along the entire length of
the leaf, although the rest of the leaf may appear normal. These stripes seem to be
concentrations of mosaic streaks. Later, the leaf tissue exhibiting the chlorotic
stripes may die, although the rest of the leaf will
remain viable. In some cases, reddish-purple streaks
extending the length of the leaf may occur in part or all of the band.
HPD may also stunt and weaken plants’ root systems. In 1993, plants in severely
diseased fields had small, rotted root systems, while adjacent healthy plants were
firmly rooted. Although the cause of this root rot was not determined, its severity
may well have been aggravated by the new disease.
Disease spread
Researchers discovered in 1994 that HPD was spread by the
wheat curl mite vector (Aceria tosichella)
which also spreads wheat streak mosaic virus (WSMV) and the wheat spot mosaic
agent. Mixed infections of WSMV and the HPD agent frequently occur, since the
vector is the same for both diseases. This mite, so small it can only be seen with
10X magnification or more, is cream colored, cylindrical, and wingless. Wheat curl
mites depend on air movements for dispersal. Since these mites can not survive
more than about a day without a living host plant, they must move over a “green
bridge” from one living host to another within a short time. In at least one case in
Idaho, corn growing near a wheat field had a high incidence of disease near the
wheat field, but that incidence diminished as the distance from the wheat field
increased.
Hosts
Information about the reaction of corn varieties to HPD is limited. Many popular
varieties are susceptible (Table 1).
TABLE 1. Reaction of selected corn varieties to the
high plains disease. Varieties listed are a compilation based on observations by
several workers under varying conditions.
| Susceptible |
Resistant or tolerant |
| Sweet corn varieties |
| Ambrosia |
Delectable |
| Challenger |
Empire |
| Crisp'N Sweet |
Gemini |
| Del Monte DMC 20-3 |
Imaculata |
| Del Monte DMC 20-10 |
Incredible |
| Double Gem |
Platinum Lady |
| Extra Sweet |
Silver Queen |
| Honey and Pearl |
711 |
| How Sweet It Is |
| Native Gem |
| Phenominal |
| Shasta |
| Style Sweet |
| 710 |
| Dent corn hybrids |
| Golden Harvest 2544 |
| Funks 4292 |
| ICI 8310 |
Host Range
In addition to sweet corn and field (dent) corn, wheat, barley, and several grasses
(yellow foxtail, green foxtail, barnyard grass, prairie cup grass, and knot root bristle
grass) are hosts of the HPD agent. HPD has occurred widely in wheat grown in the
Panhandle region of Texas, but a 1994 survey of winter wheat in southern Idaho’s
Jerome and Gooding Counties, in the vicinity of the previous year’s diseased corn
fields, revealed only two affected plants, one each in fields at least five miles apart.
Although barley seedlings in a greenhouse study were killed when mites carrying the
causal agent of HPD were transferred to them, there haven’t been any reports of
affected barley fields. In Kansas, HPD is commonly found in yellow foxtail and
occasionally found in green foxtail.
Control
No specific control measures are known for HPD, but measures similar to those for
wheat streak mosaic are thought to be helpful. The key is to break the green bridge
and prevent spread of the disease to corn and other hosts: 1) plant corn early; 2)
control volunteer wheat and grassy weeds which may harbor the mite and/or the
disease agent; and 3) plant resistant varieties when they become available.
Acknowledgments
The author thanks Dr. N. Robertson, formerly of Texas A & M University, for much of
the early work in the diagnosis of this new disease in Idaho and Dr. S. G. Jensen
and Dr. D. L. Seifers for recent work in diagnosis.
Similar information is also available via the University of Idaho Cooperative
Extension System as CIS 1038.
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Other sources of information on High Plains disease of corn
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