March heralds the beginning of spring, but the forecast remains cold until mid-month; apparently the Atlantic Jet Stream and a strong El Nino are responsible for this. Despite the occasional wintry shower, the outlook is drier and already the wheels are turning.
As soils begin to dry crops already look greener and soon we will also see their response to the first dose of nitrogen. Crops also look healthier as earlier manganese applications start to take effect and heavy mildew infections recede. Some early September drilled wheats have a severe gout fly infestation causing them to look ragged, these crops have already been fed to strengthen surviving tillers and in a couple of weeks they also should look much better. Non-frosty nights and actively growing, healthy crops should allow us to proceed with grassweed sprays.
On the lighter land some spring beans and cereals have been drilled; however, on heavier and wetter land there is still time to wait for the right conditions to create good seed-beds.
Field walking has revealed high disease pressure; particularly noticeable is the amount of rust on both barley and wheat. Even wheat varieties with a relatively high resistant rating to yellow rust are carrying the disease, can it be the “new” Kranich race? Whatever the cause, crops with significant infection will be treated with a triazole soon. A T0 fungicide will follow at GS30 (usually mid-March, three weeks prior to T1). This will include a dose of triazole with chlorothalonil to top up rust and septoria protection. At this time some crops may need an additional mildewicide. Strobilurins at T0 may also have a role if additional rust protection is required.
Cooler conditions will slow septoria and rust development, but there is lots of inoculum on the lower leaves to develop as the weather warms. Remember that warmth and rainfall during April has a strong influence on mid- to late-season disease pressure, so don’t play with jeopardy and keep T0 and T1 applications robust. Keeping the bottom of the canopy clean and well protected is particularly important in this era of septoria resistance and the weak eradicant activity of triazoles.
Winter barley early plant growth regulators often mixed with a T0 fungicide should be applied at early stem extension. Spring herbicide control in barley should be completed before the crop meets in the row and shades the target weeds.
From 1 March rapeseed sprays based on clopyralid for thistle and mayweed control can be applied, however, many forward crops will be beyond the safe growth stage for application (before green buds are raised above the canopy). Thankfully, where applied, AstroKerb (propyzamide+ aminopyralid) has already checked these targets and this workload is much reduced.
Cool conditions may slow rapeseed growth, but many crops will receive a light leaf spot/PGR application at green bud. Straight tebuconazole offers good light leaf spot control and growth regulation, but on the biggest canopies I will be using a specific PGR such as Caryx (mepiquat chloride + metconazole) + tebuconazole or Toprex (difenoconazole + paclobutrazol).
Winter beans should be monitored for leaf notching by adult pea and bean weevils. In dry conditions, slow growing spring crops are at greatest risk.