by Joel Bagg, Forage Development Specialist & District Sales Manager, Quality Seeds Ltd
The season so far has been challenging for many farmers that rely on producing forage. The frequent rains have been quite unrelenting. Saturated soils and even flooding has occurred. Considerable quality hayage and baleage has been made, but making quality dry hay without rain-damage or mould has been challenging. Much of the first-cut dry hay making was delayed with advanced maturity.
While the forage stands are quite variable, some of it looks “tough”. Severe potato leafhopper damage, with reduced growth as well as stunting of new seedings has occurred to alfalfa in eastern Ontario, and more recently in western and central areas of the province. Excessive rains appear to be leaching soil nitrogen and sulphur. Sulphur deficiency, with reduced growth and vigour can be observed on many yellowing stands.
Potato Leafhopper In Alfalfa
Scout your alfalfa fields for leafhopper, particularly new seedings. You can often see leafhoppers flying or “hopping” sideways, as they are disturbed when waking a field. Sweep nets and threshold levels are used to measure whether populations justify an insecticide application. If close to harvest cutting can reduce populations, but monitor regrowth in case spraying is required. Refer to “Potato Leafhopper In Alfalfa” at www.qualityseeds.ca/blog/19-quality-time-with-joel.
PLH feeding significantly reduces yield and root development, and can result in stunting. Decreased stand vigour results in slow regrowth following cutting and increased winterkill. New seedings and young regrowth are very susceptible. When stunting is severe in new seedings, stands can be permanently damaged.
Adult leafhoppers are 1/8th inch long, lime green and wedge-shaped. Leafhoppers insert a stylet into a leaf midrib and suck sap juices, injecting a toxin as they feed. The result is the “hopperburn”, which starts as a wedge-shaped “V” yellowish pattern on the leaf tips.
Figures 1 & 2 – Potato leafhopper damaged alfalfa new seeding on June 26th.
Figure 3 – On July 11th after spraying with Matador insecticide.
The use of ammonium sulphate and other sulphur sources to correct sulphur deficiency in alfalfa is becoming more common. Where sulphur deficiency has been diagnosed, many farmers are seeing a positive response when applying about 20 lbs/acre of sulphur as 80-90 lb/acre of ammonium sulphate (21N-0-0-24S) at green-up in the spring to get a full-season benefit.
With the wet, saturated soils this year, we may be seeing leaching and reduction of sulphate, making it unavailable to plants. Many stands are showing the yellowing and reduced growth symptoms of sulphur deficiency. To improve these stands, consider adding a reduced rate of ammonium sulphate (perhaps 45 lbs/acre) to bulk blended MAP and muriate of potash fertilizer applications after the next cut. Refer to “Sulphur On Alfalfa” www.qualityseeds.ca/blog/7-sulphur-on-alfalfa
Figure 4 – Where sulphur deficiency is occurring in alfalfa (left), applying sulphate can significantly improve vigour and growth (right).