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Symptoms of imidazolinone herbicide carryover on wheat and barley

By Jeremy Boychyn, M.Sc., P.Ag., Agronomy Research Extension Specialist | Alberta Wheat and Barley Commissions

For parts of Alberta, precipitation in the 2021 growing season was below average. Some farms received less than 150mm between April 1 and September 1. The low precipitation amount caused increased herbicide carryover risk for 2022. Many herbicide groups have carryover risks. However, group 2 herbicide carryover is most common. Imazethapyr (Pursuit and Odyssey Ultra/NXT) imazamox (Viper, Solo ADV, Altitude FX3, Odyssey Ultra/NXT, etc), and imazapyr (Ares SN, Arsenal, etc.) are the usual suspects.

Going into 2022, producers first evaluated total rainfall on their farm to assess carryover risk. Then, 2022 crop choices were altered for fields that received 125-150mm or less rain between June 1 to September 1, 2021. Additionally, fields that received 15mm of rain or less rain in any of those months (June to September) were also flagged as being at risk of carryover.

However, producers and agronomists who did not have fields flagged as being at risk should still monitor for group 2 carryover. Wheat and barley are more tolerant to imazamox carryover than most crops (see full crop tolerance list here). However, wheat and barley can still see group 2 damage and symptoms. Knowing group 2 carryover symptoms will help confirm carryover damage. Additionally, it can help ensure proper diagnosis of the cause of crop issues that displays similar symptoms. For example, group 2 carryover can be mistaken for wireworm damage due to patchy crop stands.

Imidazolinone carryover is more likely to occur in:

  • Low pH soils for the active ingredient imidazolinone
  • Coarse or sandier soils

If you think a crop is displaying imidazolinone carry over symptoms, the above listed areas may show worse symptoms.

Symptoms can show in small pockets (5-10 feet or less) surrounded by healthy plants (Figure 1). However, larger areas displaying symptoms are not uncommon.

Characteristics of imidazolinone carryover damage on cereals:

  • plant growth slows due to internode shortening and the plant may stop growing completely (Figure 3)
  • chlorosis (interveinal for cereals) and necrosis may occur after plant growth stops
  • in barley, interveinal chlorosis of young leaves and purpling of old leaves may occur (Figure 2)
  • interveinal chlorosis on newest leaf is common (Figure 4)

Note: imidazolinone carryover does not impact crop emergence. If you are unsure whether symptoms are attributed to imidazolinone carryover, contact your herbicide company representative or an experienced agronomist.

Figure 1: Small patches of group 2 herbicide carryover in wheat (Image courtesy of Andrew Reid, BASF)

Figure 2: Interveinal chlorosis and purpling in old leaves of barley plants due to group 2 carryover damage (Image courtesy of Eric Johnson)

Figure 3: Stunting of cereal crop (right) due to group 2 carryover. (Image courtesy of Eric Johnson)

Figure 4: Interveinal chlorosis in cereals due to group 2 injury. (Image courtesy of Eric Johnson)