Faced with Covid-19 related contraction of demand for spring barley and oats, many growers will want to take advantage of the scrapping of the three crop rule and maximise wheat area this autumn. But that will bring the risk of a disease little-known to Scottish growers: take-all.
This is according to agronomist, Eric Anderson of Scottish Agronomy who says: “The talk in both markets is of a significant reduction in demand for 2021 harvest and growers are being advised to seek alternatives. The obvious choice is winter wheat as it offers the most attractive gross margin potential.”
In Scotland, very few second wheat crops have been grown recently, so many growers are unfamiliar with the fungal disease take-all, says Mr Anderson.
AHDB estimates that half of UK wheat crops are affected and suffer average yield losses of five to 20%.
Rotation is a key driver of the disease with second and third straw crops at highest risk before ‘take-all decline’ cuts in.
“Wheat and barley are similar in susceptibility, but barley is more tolerant,” says Mr Anderson. “So, although you may think of a wheat following spring barley as a first wheat it is actually a second straw crop and therefore at risk of take-all.”
A firm seedbed discourages fungal growth and ploughing buries most of the take-all inoculum, giving seedlings time to establish before their roots reach infective soil, he adds.
“But consolidation after ploughing is vital. Min-till leaves an infective soil surface but has the advantage of leaving a firmer seedbed.”
Take-all inoculum decreases after harvest and the risk to the next crop falls as the interval between harvest and drilling lengthens.
While delaying drilling is a useful cultural control in England, it is not realistic in Scotland and having been caught out by last autumn’s weather growers will want to crack on with drilling as soon as this year’s protracted harvest is over.
“Buying certified seed of known health status, or testing seed if home saving, and judging the key diseases and risks for your crop are important first steps in getting the crop off on the best possible foot and being able to select the most appropriate seed treatment,” Mr Anderson says.
“Second or third wheat crops drilled in time to emerge by mid-October are at greatest risk from take-all, and it is in these situations the take-all specific seed treatment Latitude (silthiofam) will provide the most benefit. For first wheats there is no need for this treatment as a single year’s break continues to be the best way to minimise the disease’s impact.”
For added control of the full spectrum of seed borne diseases including bunt, septoria nodorum and microdochium/fusarium, Mr Anderson recommends Latitude is co-applied with a single purpose dressing (SPD) such as fludioxonil.
“A second precaution we advise is to have seed, whether commercial or farm-saved, tested for microdochium/fusarium. Due to the weather in the run up to harvest, microdochium levels are elevated and if your winter wheat seed result comes back from testing with greater than 10% infection, an SPD is essential. Your merchant will have tested seed for germination but not necessarily for seed borne microdochium/fusarium, so you have to specifically request it.”