Manitoba Insect & Disease Update: June 23, 2015

 
Summary
  
Scout cereal crops for rusts, and consider whether fusarium is a risk. Insect feeding has been minimal in cereals, however watch for signs of feeding or larvae of cereal leaf beetle so we can assess levels of parasitism if these are present.
 
In canola, flea beetles are becoming less of an issue as canola advances beyond the susceptible stages and flea beetle populations decline.
 
In forage crops, alfalfa weevil continues to be at high levels in some alfalfa fields in the Interlake and Northwest areas.
 
Cutworms are also becoming less of a concern as crops advance and cutworms begin to pupate. Grasshoppers are emerging and it is good to start assessing populations around field edges.
 
Cereal Crops 
 

Cereal Crops Pathology report submitted by Pam deRocquigny, Cereal Crops Specialist, MAFRD


Stripe Rust and Leaf Rust: After the first reports of stripe rust and leaf rust in winter wheat last week, there have been additional reports of stripe rust and leaf rust in spring wheat fields near Altona, MB and along the US/Canada border.  For wheat fields approaching the flowering stage, this is the key timing for a fungicide application to manage Fusarium head blight. A fungicide at this timing will also help protect the flag leaf from leaf diseases such as stripe rust or leaf rust. However, an earlier fungicide application targeting the flag leaf timing may be needed if leaf or stripe rust infections become visible on the flag leaf prior to heading. 

 
Keep in mind both leaf rust and stripe rust can increase rapidly when susceptible varieties are grown and weather conditions are favorable for rust development (i.e. disease triangle). For information on leaf rust and stripe rust resistance ratings in spring wheat varieties, and leaf rust ratings in winter wheat varieties, refer to Seed Manitoba 2015 at www.seedmb.ca. For stripe rust resistance ratings in winter wheat varieties, refer to www.cropchatter.com.
Producers and agronomists should continue to scout both winter and spring cereal crops for rusts and report any finds to MAFRD so that the locations of these diseases can be shared with others.  Monitoring, early detection and reporting of rust will improve disease management outcomes.
 

 Figure 1. Stripe Rust.

Physiological Leaf Spot: There have been suspected cases of physiological leaf spots (PLS) in winter wheat in the province. This is not an uncommon issue in winter wheat, especially when we’ve had growing conditions which favour its development including cool, wet spring and summer conditions that promote vigorous plant growth. Physiological leaf spot symptoms start as small yellow necrotic spots (one to three mm) on the upper leaves. As they develop, a dark brown center forms in this necrotic spot, which is similar to tan spot. However, physiological leaf spots are usually more “blocky” or “angular” and are often defined by the leaf veins. Proper diagnosis of the disease is key to prevent any unwarranted fungicide applications as PLS is not caused by a pathogen. Additional information on PLS can be found in the Current Crop Topics section of MAFRD’s website at https://www.gov.mb.ca/agriculture/crops/seasonal-reports/current-crop-topics.html
 
Cereal Leaf Beetles: Low levels of feeding by cereal leaf beetles have been noted in some fields in the Central region, and a couple of samples have had larvae submitted for testing of parasitoids so we can judge how well the parasitoid Tetrastichus julis is establishing and spreading. So far only 1 sample, from the Austin area, has been processed, and 8 of the 9 larvae submitted contained the parasitoid. This is very encouraging, especially considering the closest release of parasitoids was in the Treherne area.
 
Agronomists and farmers are encouraged to collect and submit larvae for parasitoid testing should they find them in fields of cereal crops or forage grasses. Refer to the June 16, 2015 Manitoba Insect and Disease Update for instructions on sending larvae for parasitoid testing, or contact John Gavloski at the contact information at the bottom of this update.
 
Figure 2. Cereal Leaf Beetle                                                          Figure 3. Feeding by Cereal Leaf Beetle.
 
Insects in Multiple Crops
 
Grasshoppers: Emergence of grasshoppers has started and there have been a couple of reports of high levels of nymphs emerging. In Manitoba there are 4 species of grasshoppers that potentially can be crop pests, and in the past few years twostripped and migratory grasshopper have been our more abundant species. Both these species overwinter as eggs, and much of the egg hatch will occur over June. The egg hatch can be quite staggered though, occurring over a period of a few weeks. 
 
Newly emerged grasshoppers are quite small, about the size of a wheat kernel when they first hatch, and get progressively larger as they go through their 5 juvenile stages. They do not fly until they reach the adult stage, which is often well into July, and depends on temperature. So when scouting for young grasshoppers, look in the vegetation close to the ground to see what is present.
 
If populations are quite high along field margins, and it looks like control may be needed, a general recommendation is to wait until many of the grasshoppers have grown into their third (out of 5) stage of growth as a nymph, when wing buds would just be starting to be noticeable. At this stage the grasshoppers still cannot fly, and most of the eggs would have hatched. Do keep an eye on how much defoliation is occurring to crops along the field edge though. How many and how quickly they move into the crop often depends on how lush and attractive the vegetation is where hatch occurred. Bran baits as well as foliar sprays are available for grasshopper management.   
 
Also note when scouting for grasshoppers in the field edges that there are other insects such as leafhoppers, usually non-economical species, that may be present in these areas that will hop when disturbed. So look carefully so proper identifications are made. Although aster and potato leafhoppers can be pests of crops in Manitoba when abundant, the rest of the roughly 360 species of leafhoppers in Manitoba are not pests of crops. Some species can be abundant in the vegetation surrounding fields outside the crop. Be careful not to confuse them with grasshoppers. The photo below is of a small grasshopper (left) and one of the non-economical species of leafhoppers (right). Note the highly pronounced back legs of the grasshopper, and longer antennae. The leafhopper in the photo has wings fully developed while the grasshopper is wingless.
 
Figure 4. Grasshopper nymph (left) and leafhopper (right) 
 
Insect Monitoring Programs
 
Diamondback Moth: Diamondback moth monitoring with the pheromone baited traps is now completed. Table 1 below summarizes the highest counts in each region in Manitoba. Notice that the high counts do vary with region, for example counts were higher in the northwest than southwest. However, overall counts were not exceptionally high, and were lower than those in 2014. The table below and full summary can also be found at: https://www.gov.mb.ca/agriculture/crops/insects/diamondback-moth-forecast.html
So far only low levels of larvae of diamondback moth have been found. 
 
Table 1. Highest cumulative trap counts per region over the trapping period (April 26 to June 23, 2015):
Location Count
Northwest
   The Pas 159
   Swan River 112
   The Pas 86
   The Pas 78
Southwest
   Alexander 40
   Douglas 35
   Mather 31
   Carberry 30
Central
   Kane 173
   Portage la Prairie 156
   Morris 147
   Rosenort 108
Eastern
   Steinbach 112
   Ste. Elizabeth 91
   Tourond 59
   Beausejour 40
Interlake
   Faulkner 134
   Grahamdale 64
   Eriksdale 46
   East Selkirk 18
 
Bertha armyworm: Moths of bertha armyworm are just starting to emerge. Many traps have not recorded any yet; a few traps have caught very low levels (less than 20).  

Compiled by: 
 
•John Gavloski, Entomologist
Manitoba Agriculture, Food and Rural Development
Phone: (204) 745-5668
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.
 
To be placed on an E-mail list so you will be notified immediately when new Manitoba Insect and Disease Updates are posted, please contact John Gavloski at the address or numbers listed above.

Manitoba Insect & Disease Update: June 23, 2015