Sunflower growers should scout their fields for sunflower rust, sclerotinia head rot, lygus bugs and the banded sunflower moth, says Anastasia Kubinec, oilseed specialist with Manitoba Agriculture, Food and Rural Initiatives.
The four pests can affect sunflower yield and quality, especially in confectionery sunflowers where the seed is sold for human consumption.
“You have to be in the crop looking at what’s going on before you know what the issues really are and if it’s time to do something about them,” Kubinec said during an MAFRD webinar July 30.
Sunflower rust was bad in 2008 and 2009, she said. There was some in 2010 and pockets in 2013.
Sunflower rust is specific to sunflowers and cyclical so it can be reduced through crop rotation.
Farmers should try to find out the crop and disease history in fields adjacent to their sunflower fields. The fungal disease overwinters in sunflower residue. Spores can be produced and infect nearby sunflower fields.
Sunflowers are most at risk at the early- to mid-bloom stage, Kubinec said.
Infected leaves have cinnamon-coloured spots. The infection will start on the lower leaves, but can move up.
“The critical time when rust can affect the plant is at R4, where the head is still somewhat closed but you can see the odd little ray petal, to the end of R5 when your flowering and pollination have occurred,” Kubinec said.
“If you are seeing it on the lower leaves keep a close eye on it as it moves up.
“You’re not wanting to pull the trigger (and apply a fungicide) until the top four leaves are affected.”
A fungicide should be applied when only about one per cent of the leaves are infected.
Skip spraying if the top leaves are infected at R6 stage when the ray petals are starting to wilt off the head. The crop has advanced enough that the disease won’t have much effect on yield, she said.
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Sclerotinia head rot — the same fungal disease that attacks canola — is often a problem because there’s so much inoculum around. Even if a susceptible crop such as sunflowers or canola haven’t been grown in a field for several years, disease ascospores can easily migrate from other nearby fields, causing infections if humidity is high in the crop.
In 2012, a fungicide was registered for control of the disease in sunflowers, but like in canola, it must be applied before the crop is infected.
Farmers need to assess the risk to their crop and whether the crop is worth protecting, Kubinec said. Factors to consider include whether susceptible crops were grown in recent years in that field or nearby and if the crop canopy is humid.
Head rot ascospores need moist conditions as well as sunflower pollen to feed on, Kubinec said. That’s why a fungicide needs to be applied before a lot of pollen is produced.
“If you’re spraying for head rot at R3 it’s probably a bit too early,” she said. “If your flowers are already done pollinating it’s probably a little too late. What we do target is that R5.1 to 5.2.”
MAFRD has a sclerotinia assessment tool for canola and hopes to soon post one for sunflowers on its website, Kubinec said.
Sunflowers staging varies a lot this year. Kubinec said two weeks ago fields she had seen varied from R3 to R5.5.
“Where you really do want to pull the trigger specifically for that head rot fungicide application is when 50 to 80 per cent of that field is at R5.1 to R5.2,” she said. “Any earlier you’re probably not having a lot of that pollen and later will be too late.”
Controlling head-attacking insects is critical in confectionery sunflowers, Kubinec said.
The farmer first needs to accurately identify insects he or she sees in their crop. Some insects are beneficial because they attack harmful insects.
The economic threshold for controlling lygus bugs in confectionery sunflowers with an insecticide is one insect per nine sunflower heads, Kubinec said.
The ideal crop stage for control is between R4 and R5.1. That’s earlier than ideal for sclerotinia control, but the two sprays can be applied then, Kubinec said. The farmer just needs to decide which pest poses the most risk — lygus or sclerotinia.
Farmers should spray sunflowers to control the banded sunflower moth when there are at least two per head. (The adult moth lays its eggs on the sunflower and it’s larvae feeding on the seed that does the damage.)
The moth is whitish to brown in colour with a distinct black to dark-brown triangle on its back. They will be more prevalent on the edges of the field.
“Try to time your scouting at dusk or dawn,” Kubinec said.
They are more active when it’s cooler.
The ideal crop stage to control the adult moth is R4 to R5.1.
“That’s when you’ll want to be keeping track of those insects,” she said.