Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu
In the last issue of the Weekly Crop Update, two causes of premature vine decline in potatoes were presented. It was reported that Early Dying Syndrome caused by the verticillium fungus was confirmed in potato samples from Delaware. This problem is worsened if lesion nematodes are present. Air pollution (ozone) damage, which can be a problem in varieties such as ‘Red Norland’, was also detailed.
Recent reports from growers indicate that some varieties have declined rapidly in the past two weeks. In addition to the Early Dying Syndrome and ozone damage there may be additional reasons for vine decline. There are a number of diseases other than Early Dying Syndrome that can lead to vine decline including seed piece decay (leading to weaker plants); Fusarium, Rhizoctonia, and aerial blackleg diseases; and a number of viruses.
Heavy European corn borer damage can cause portions of vines to die and excessive Colorado potato beetle damage can cause added stress on plants leading to decline.
Injury by wind, wind-blown sand, or hail can open up wounds in potato vines that then can be infected by secondary bacterial and fungal invaders setting up conditions for vine decline. Senescence of lower leaves in heavy vining varieties due to shading can also be a wound source. Hot weather will speed up losses by these secondary invaders on wounded plants.
Fertility problems, such as inadequate nitrogen and excessively low pH can be factors. Nitrogen deficiencies occur commonly in heavy soils through denitrification losses in areas that had periods of water-logging and in sandy soils that had heavy leaching rains. I have seen low pH (below 5.0) cause stunting and reduced plant health in large areas of potato fields. Excessive salt and salt injury from fertilizers banded near potatoes is another cause of extra stress, especially in sandy soils and can be a contributor to reduced plant longevity.
Variety and temperature interactions are also critical. One of the varieties now being grown for early acreage in Delaware is ‘Envol’. This variety was bred and selected in Quebec, Canada and released in 1999. It is moderately susceptible to verticillium wilt and rhizoctonia and susceptible to late blight and common scab. It is rated as very early. A variety such as ‘Envol’ will have a quick decline naturally after tubers have bulked up. Hot weather and water stress can often lead to vine decline in these very early varieties before tuber bulking has completed. ‘Envol’ is a Canadian potato bred under cooler growing conditions than Delaware. Our Delaware environment gets much hotter during critical growth stages than Canada and extended high temperatures in June may lead to early vine decline.
It is important to understand variety characteristics as they relate to the potential for premature vine decline including breeding background, area of adaptation, maturity, and disease susceptibility.