Manitoba Insect and Disease Update: July 16, 2014
Compiled by:
- John Gavloski, Entomologist
Manitoba Agriculture, Food and Rural Development
Phone: (204) 745-5668
Fax: (204) 745-5690.
- Vikram Bisht, Plant Pathologist
Manitoba Agriculture, Food and Rural Development
Phone: (204) 745-0260
Fax: (204) 745-5690
To report observations on insects or plant pathogens that may be of interest or importance to farmers and agronomists in Manitoba, please send messages to the above contact address.
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Summary
Flowering canola crop needs to be protected against white mold since there have been many rain events lately, Phytophthora root rot of soybean has started showing up, especially in flooded fields. Early lesions of sunflower rust have been found in a 2nd location. Alfalfa weevil levels were quite noticeable in some alfalfa fields, but they are now starting to pupate, so levels are declining.
Alfalfa
Severe leaf spotting of alfalfa was observed at the University of Manitoba Carman Research Farm (Fig 1). Cool temperatures and frequent spring rains are favorable for the development of foliar diseases. High levels of the diseases can cause early defoliation.
Alfalfa Weevil levels were high in some fields over the past few weeks. Early cutting, when practical, is an effective and cheap way of managing alfalfa weevil in hay crops. Populations are starting to turn to pupae now, so larvae and feeding should decline.
Fig.1. Common leafspot disease is favoured by frequent Fig. 2. Larvae of alfalfa weevil
rains and can cause severe defoliation. Photo: John Gavloski, MAFRD
Photo: Vikram Bisht, MAFRD
Canola
Flowering canola needs to be protected against white mold disease. Many fields are in the critical stage with max flowering (30%+) and conditions are favourable for ascospore production and release. Last year’s fields, with sclerotinia disease hosts, could be carrying potential inoculum in the form of sclerotia. Germination sclerotia with open apothecial discs (Fig 3) can be seen in some dense wheat fields with very high within crop canopy moisture. Under conditions of strong winds with rain, ascospores can be easily dispersed to canola or other susceptible host crops.
Fig.3. Apothecia on wet soil in thick wheat canopy. Fig.4. Germinating Sclerotia in wheat canopy, found Photo: Vikram Bisht, MAFRD. by David Kaminski. 2014.
Photo: Vikram Bisht, MAFRD.
Levels of larvae of diamondback moth have been low across most of Manitoba, with the exception of some canola fields in the Stead area. This is the area that had some of the higher trap counts earlier in the year. We are currently starting to see some pupae of diamondback moth, so the larval numbers that are present may decrease as they start to turn to pupae.
Fig. 5. Diamondback moth pupa (left) and larva (right).
Flax
Wilting plants of flax were seen in Carman Research Farm. The roots and stems of Fusarium infected plants showed vascular browning, when cut longitudinally.
Fig.6. Fusarium wilt of flax, Carman, 2014. Fig.7. Cross section of flax stems with Fusarium wilt, Carman Photo: Vikram Bisht, MAFRD Photo: Vikram Bisht, MAFRD
Soybean
Phytophthora root rot has started appearing in a few fields (Fig 6, 7) especially those with excess moisture and standing water for a few days. Typical symptoms include drying plants with leaves still hanging on, and stems with dark brown discoloration from below the soil line.
Fig.8. Phytophthora root rot infected, two plants on left and Fig.9. Phytophthora root rot infected plants with
Fomesafen (Reflex) injury on foliage on plants on the right. leaves still hanging on – typical diagnostic
Photo courtesy: Vikram Bisht, MAFRD symptom of the disease. 2014, Elm Creek
Photo: Vikram Bisht, MAFRD
Sunflower
Rust spots have been found again in sunflowers; this time from Elm Creek area (Fig 10, 11). These spots could produce brown to dark brown uredial pustules later in the season.
Fig 10, 11. The aecial cups seen on the underside of the sunflower leaf, and same spot on the upperside of the leaf. Photo Courtsey: Troy Turner, National Sunflower Association of Canada.
Wheat
Curling flag leaf, but no leaf tip chlorosis was seen in a field – the sign appears to be boron deficiency. The diagnosis is based on the symptoms produced in my Crops Diagnostic School Demonstration using hydroponics NFT beds to develop nutrient deficiency, including boron deficiency in wheat (Fig 12, 13).
Fig 12, Flag leaf curling in wheat field. Fig. 13.Boron deficiency developed using hydroponics NFT technique, shows flag leaf curling – Vikram Bisht, MAFRD, 2010 Crops Diagnostic School.
Fig 14. Winter wheat showing FHB, Winkler. Fig 15. Winter wheat heads showing FHB, Photo courtesy Tao Wang, CargillAgHorizons . from 15% to 100% spike infection.
Photo Courtsey Earl Bargen,MAFRD.
Minute leaf spots are showing up on flag leaves in spring wheat; some of the fields are just about to reach the critical FHB sensitive stage. If the forecasts indicate that the critical flowering period will coincide with high FHB risk – then FHB control fungicide application will be helpful. If the forecast risk for FHB is low (based on weather or flowering), then a flag leaf application could be considered, depending how the lower crop canopy and the flag leaf look - with respect to leaf diseases. Warm and humid conditions can still favour leaf diseases.
The FHB risk forecast for the whole province has been low to moderate for a few days around July 11; but after rains in the weekend the risk increased again (12 -14 July) especially in the eastern half of the province; near the lake region was high to extreme. The risk on Jul 16 is low in the western MB to moderate in eastern MB.
Emergence of Wheat Midge
The following maps show the emergence of wheat midge and its key parasitoid Macroglenes penetrans. So far there have been no reports of high levels of wheat midge in Manitoba, and emergence may still be in the early stages in northern Manitoba and the northern Interlake.
A reminder that once wheat has flowered (produced anthers) it is no longer an acceptable host for wheat midge and scouting for wheat midge would not be necessary in these fields. Wheat midge that are present would still be flying in these fields, but the crop is no longer an acceptable host for the larvae.
Also note that the emergence of the parasitoid is synchronized quite well with that of the wheat midge. So hopefully when the wheat midge are emerging the parasitoids will be waiting to lay their eggs into the eggs of the wheat midge.
