High Plains disease

In early infection stages, plants exhibit stunted growth and poor tillering, often resulting in a dwarfed appearance. Depending on the infection timing and the specific wheat cultivar, leaf tips may prematurely wither, turn necrotic, and curl.

In corn, symptoms include yellow streaks running parallel to leaf veins, accompanied by overall development suppression. These visual symptoms can sometimes be mistaken for nutrient deficiencies, complicating field-level diagnosis.

Heavily infected plants often fail to produce productive spikes or may develop shriveled, underdeveloped kernels. In severe cases, the infection can lead to complete plant death before the jointing stage.

In the field, the disease typically manifests in patches, as the virus is spread by localized colonies of mite vectors. The resulting field appearance is characterized by a patchy or mottled green-yellow mosaic.

The pathogen responsible for High Plains disease is the High Plains virus (HPV), a member of the genus Emaravirus. It is a segmented RNA virus that primarily infects winter cereals and maize.

The primary vector for the virus in nature is the wheat curl mite, Aceria tosichella. These mites acquire the virus while feeding on infected plants and remain capable of transmitting it to healthy plants for the rest of their lives.

The virus persists in winter wheat crops, perennial grassy weeds, and volunteer wheat. This makes the "crop-weed-vector" bridge critical for the survival of the pathogen during the off-season.

The vector is highly mobile, easily transported by wind over significant distances. This ensures rapid virus dissemination within a field under favorable climatic conditions.

It is important to note that the virus is not seed-borne or soil-borne in the traditional sense; transmission occurs exclusively through the feeding activity of eriophyid mites. The virus biology is inextricably linked to the mite's life cycle.

Disease development is highly dependent on the population density of the wheat curl mite. A warm, dry autumn facilitates rapid mite reproduction and early infection of winter wheat seedlings.

The autumn period is the most critical window for infection, as volunteer wheat acts as a bridge for virus transfer from harvested fields to new winter wheat seedlings. Higher temperatures prolong mite activity and migration.

The presence of infection reservoirs, such as perennial grass weeds near fields, significantly increases the risk of epiphytotics. Lack of spatial separation between wheat and corn fields promotes cross-infection.

Spring warming triggers renewed mite activity, potentially leading to secondary infection outbreaks. However, the most severe crop losses occur when plants are infected during their earliest developmental stages.

Agronomic factors, such as delayed winter wheat sowing or poor volunteer wheat management, create an ideal environment for the mass proliferation of the vector and the spread of the virus.

The primary economic danger of the disease is a sharp reduction in yield, which can exceed 30–50% in cases of early infection. Plants become weakened and significantly more susceptible to secondary pathogens.

The virus negatively impacts grain quality by reducing thousand-kernel weight and grain plumpness. This results in the loss of market grade and reduced nutritional value of the harvest.

Infected crops often become economically unviable due to high input costs relative to the significantly reduced output. In some instances, entire field sections may require destruction by tillage.

High Plains disease complicates crop production systems, as the virus can accumulate in crop cycles where corn follows wheat. This poses a long-term risk for rotational planning in intensive agricultural operations.

Indirect harm occurs through the suppression of root systems, which limits the plant's ability to uptake water and essential nutrients from the soil, effectively making the crop more vulnerable to drought stress.

Effective control is centered on eliminating the "green bridge" for the vector. It is recommended to thoroughly destroy volunteer wheat in fields at least 10–14 days before planting winter wheat.

Adhering to optimal planting dates for winter cereals helps minimize the risk of mass mite flights and feeding on young, vulnerable seedlings. Early-planted crops are at the highest risk of infection.

While the use of acaricides during early vegetative stages can suppress mite populations, this approach is often not economically justified and difficult to execute due to the microscopic size of the pest.

Utilizing genetically resistant or tolerant wheat cultivars remains the most promising long-term strategy. Breeding for resistance to both the virus and the mite vector significantly lowers infection risks.

Spatial isolation of wheat crops from corn fields is an important management element. Furthermore, aggressive control of grassy weeds, which serve as virus reservoirs and overwintering sites for the mites, is essential.