VEGETABLE CROP UPDATE

Feature Pages of the Week:
Photos and descriptions of herbicide injury on tomatoes
Find these on the Tomato, Pepper, & Eggplant index page under “Pest Management – Weeds”.

Herbicide Injury Symptoms in Tomatoes - PPI and PRE Herbicides http://www.omafra.gov.on.ca/english/crops/facts/info_herbicide2.htm

Herbicide Injury Symptoms in Tomatoes - Postemerge Herbicides
http://www.omafra.gov.on.ca/english/crops/facts/info_herbicide.htm

Where to find vegetable variety trial information
Find this on any of the vegetable index pages under “Crop Management”

http://www.omafra.gov.on.ca/english/crops/facts/vegtrial.htm

   Copper Fungicides Registered On Tomatoes and Peppers

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   Research Update: Callisto Recropping Interval in Tomatoes

Darren Robinson, Ridgetown College – University of Guelph

Recently, Callisto was registered for residual control of broadleaf weeds in field, seed and sweet corn.  Many growers are considering how this product fits in rotation with many high-value crops, including tomatoes.  Research has been conducted over a number of years at Ridgetown College and in growers’ fields to determine the potential for carryover onto tomatoes.  We’ve found that as long as growers wait 11 months after applying Callisto, tomatoes can be safely grown the next year.  The rotation of tomatoes with an 11 month interval following Callisto recently met PMRA requirements for registration, and is in the process of being added to the label.  Editor’s Note:  The 11 month recropping interval is now on the Callisto label.

   Powdery Mildew Control for Peppers in the Transplant Greenhouse

In 2005, pepper powdery mildew was found in a number of fields in Essex and Kent.  There are no fungicides registered to control this disease in the field, but to prevent initiation of an infection in the greenhouse, several products are available:  Nova (myclobutanil), microscopic sulphur, and the newly registered Milstop (potassium bicarbonate).  Rotate between these products to avoid the development of resistance.  Nova can be used at 12-day intervals, microscopic sulphur at 14-day intervals, and Milstop at 7-day intervals.

Powdery mildew is easy to miss during scouting, until it is very severe, as the symptoms develop on the underside of the leaves.  Although powdery mildew typically appears as a white powdery growth on most plants, it may actually appear brown on pepper leaves.  As the disease progresses, the upper leaf surface may develop yellow spots, eventually turning completely yellow and dropping off in severe cases.  Symptoms appear on older leaves first.

The pathogen that causes powdery mildew in peppers has a wide host range, which includes tomato, however it has not been found to infect tomato in our growing region.  Powdery mildew found infecting tomato in the northeast U.S. and Ontario has been caused by a different organism.  Yet another organism causes powdery mildew of cucurbits.  The organisms infecting tomato and cucurbits can produce spores on both the upper and lower leaf surfaces.

Powdery mildew of peppers can develop over a wide range of temperatures in low or high humidity conditions.  Due to its wide host range, it can be difficult to control with cultural practices.  It was first identified in the northeastern U.S. in the mid to late 1990s, although it has been present in Florida in 1971.  In Florida, California, and other southern areas, it can cause heavy yield losses due to defoliation and the resulting sunscald.

Photos of the disease can be found at http://www.avrdc.org/pdf/pepper/powdery.pdf and http://vegetablemdonline.ppath.cornell.edu/NewsArticles/PepperyPowdery.htm.

   Caterpillars on Tomato Plants

I’ve started to find some variegated cutworm larvae in tomatoes, ranging in size from less than ½” to well over an inch long.  If you haven’t started intensive scouting down in the canopy, now is the time.  If possible, scout early in the morning or towards evening, when they are more likely to be up feeding in the canopy rather than hiding in the soil.  Look for signs of leaf and fruit feeding.  Shake the plant and look on the soil underneath the plant to see the larvae.  Treatment thresholds will depend on the end-use of the tomatoes and how much fruit damage can be tolerated.

Tobacco hornworms are also present in many fields.  Small larvae make holes in leaves, while larger larvae will strip the foliage, leaving the thicker leaf stems bare.  They also feed on fruit.  The hornworms can be surprisingly hard to spot, however, and are hard to shake off the plant.  Although a hornworm can eat a lot, they are not usually present at high levels.  In “Vegetable Insect Management” (Foster & Flood, Meister Media), the authors recommend counting the number of worms per 10 plants in the damaged area of the field.  If the count averages more than 1 hornworm per 2 plants, they suggest an insecticide application to that part of the field.

Low levels of cabbage loopers are also present in some fields.  They feed on the leaves, but rarely on the fruit.  Looper cocoons, however, may be found attached to the fruit.  Treatment may be needed if defoliation exceeds 20% or to avoid contamination of fruit by numerous cocoons.  I find it easiest to locate the loopers by looking under the leaves with the freshest looking damage and frass.  You may find some by shaking the plant, too.

Variegated cutworm damage and frass

Cabbage looper damage                                  Hornworm damage and frass

   Aphids

In some fields, high aphid populations have developed.  When making decisions on whether an insecticide is necessary, there are several factors to consider.  The first is – how many live aphids are present?  Always look closely.  You may see a lot of white skins left from aphids molting and brown, swollen-looking parasitized  aphids (known as “mummies”), as well.  Look closely to see how many live aphids are present.

In Vegetable Insect Management (Foster & Flood), the author suggests checking the leaf below the highest open flower on 30 randomly selected plants.  Count the leaf as infested if any live aphids are found.  If 50% of the leaves are infested during the period from 6-8 weeks before harvest, they suggest treating the field.  At these levels, there could be enough aphid feeding to impact crop production.

If there’s a good rainfall before you get to the field to spray, scout again, as the rain often reduces aphid populations.  It can wash them away and knock down aphid flights, but damp conditions also promote fungal infections of the aphids.  You may notice dead aphids with fungal growth on them.

Another factor to consider is natural enemies.  If the population of natural enemies, such as lady beetles, syrphid flies (larvae shown in photo), parasitic wasps, and lacewings, has built up, they will kill a lot of aphids.  Insecticide applications will kill these beneficial insects, but the aphid population will rebound more quickly than the population of natural enemies.

Don’t bother using insecticides to try to control virus transmission by aphids.  The common aphid-vectored tomato and pepper viruses in Ontario are spread as soon as the aphid probes a leaf on an uninfected plant after feeding on an infected plant.  There is no way to spray enough insecticide to keep infected aphids from probing.  Even soybean aphids may probe tomatoes or peppers while passing through searching for soybeans.  If they previously probed an infected crop plant or weed, that’s all it takes to spread the virus.

   Monitoring Migrating Moths

Tomato pests like tomato fruitworm (corn earworm) and variegated cutworm move in on weather systems from areas to the south.  Well, the worms don’t – it’s the moths that get blown around by the wind.  How yucky if the wind blew the worms around.  It is nice to know when the moths arrive, so that we can save our intensive scouting for the actual times their damaging larvae are likely to be present.

High variegated cutworm moth populations were being found by late July, so it was time to start looking closely for larvae and their damage.  Reports from nearby regions indicated that high corn earworm (tomato fruitworm) moth populations were being captured in monitoring traps.  Although they are not usually a cause of widespread damage in tomatoes, they do burrow into fruit, rendering it unmarketable.

If you don’t have pheromone traps set up on your farm, there are a few sites on the internet that can give you some information on pest movement.

Corn Earworm (Tomato Fruitworm):  http://www.ent.iastate.edu/trap/cornearworm/

Click on “Trap Summary” at the left side of the page to access trap counts for 7 Midwest and North Central states plus Ontario.  This is part of a large regional project to monitor corn earworm flights and test populations for resistance to insecticides.

Migration Forecasts for Corn Earworm and Other Migratory Moths:  http://www.maplecity.com/%7Esand/cew/imrf.html

The movement of insects (like corn earworm and variegated cutworm) from the south can be predicted.  When there is a certain configuration of high and low pressure cells to the south, an “insect pump” is created, which lifts the insects and moves them to a “drop zone”.  This is explained very well in the book “Vegetable Insect Management” edited by Rick Foster and Brian Flood (MeisterPro Publishing).  Back in 2001, the media noticed this effect when soybean aphids invaded Toronto during a ball game at the SkyDome.  They were in the “drop zone”.

At this website, you can get a 1-5 day forecast of the risk of insect migration into your area.  Here’s the Aug. 13-15 forecast, showing a moderate risk of insect migration into southwestern Ontario.  Actually the map stops at the border, but the insects won’t, so I’m extrapolating.

   Pseudomonas on Peppers

In mid-July, I was called to a pepper field due to severe spots and yellowing on bell and shepherd pepper plants.  I sent samples to the Pest Diagnostic Clinic at the University of Guelph and they found Pseudomonas syringae pv. syringae.  This may sound familiar because it is Pseudomonas syringae pv. tomato that causes bacterial speck of tomato.  There isn’t a lot of information to be found about this disease, but it doesn’t seem to cause fruit lesions and the plant likely “grows out of it” once conditions become less favourable for the pathogen.  Pseudomonas syringae pv. syringae prefers temperatures of 16-24°C (61-75°F) and high humidity.

   European Corn Borer

European corn borer development can be predicted by looking at growing degree day accumulation.  The base temperature for ECB growth and development is 10°C, so we need to look at GDD10 accumulations.

According to insect development models, the 2^nd generation corn borer larvae hatch from about 1,050-1,400 GDD10 with the peak around 1400.  By Aug. 21 in Windsor, 1,285 GDD10 had accumulated.  That meant at that point, almost all of the 2^nd generation egg laying was complete, over 50% had hatched, but less than 25% had reached the 4^th instar.  In Delhi, where 999 GDD10 had accumulated, over 50% of the 2^nd generation moths had emerged, but very few had laid eggs yet.  Bottom line?  Keep on with your insecticide program to protect your peppers.

Could there be a partial third generation?  The earliest of the 2^nd generation larvae would reach the 5^th instar (last larval stage before pupation) at around 1,325-1,550 GDD10, with the peak around 1,950 GDD10.  Then they would have to pupate, emerge, mate, and lay eggs.  Once those eggs hatched, we would have larvae present again.  For review, here’s a simple GDD chart for predicting moth flights and the map of the ECB regions of Ontario.

Growing Degree Days (base 10°C) Required for First Catch and Peak Flight
Activity of ECB in both Univoltine and Bivoltine Regions of Ontario

Map Showing ECB Distribution in Ontario
(Canadian Corn Pest Coalition, www.cornpest.ca)

There’s some excellent information on European corn borer on the Ontario Weather Network website.  They refer to work by R.J. MacClanahan, a former researcher with Agriculture Canada in Harrow.  His work in the 1970s and 1980s showed that a 3^rd generation of ECB occurred in 6 of the 14 years they monitored and that in those years, over 1,260 GDD10 had accumulated by Sept. 10.

In 2006, Windsor had accumulated 1,496.2 GDD10 by September 11.  Vineland was just under 1260 GDD10.  The other locations listed were still below 1200.  The long term average accumulation for Windsor by September 11 is 1,312.5 GDD10 since April 1.

   Stink Bugs

Surprisingly high populations of stink bug nymphs and adults were present in many tomato fields in the fall of 2007.  As the vines declined, it was quite easy to spot them crawling on the fruit.  Even late in the season, they can still cause damage, so continue scouting until harvest.

Stink bug is listed on the Sevin label, but be aware that it is not considered effective on this pest.  Azinphos-methyl (Guthion) is no longer registered on tomatoes.  If you are spraying endosulfan (Endosulfan, Thionex, Thiodan) or cyhalothrin-lambda (Matador) for other pests, you may notice a reduction in stink bug numbers, however.  Remember to observe the pre-harvest intervals on the pesticide labels (see summary below).

Always read and follow the pesticide label.

Stink bug nymph                                 Stink bug nymph feeding                    Stink bug adults

   Agricultural Equipment on the Road – Information on Safety, Legislation

Some of you may know this, but the Farm Safety Association has a manual called The Safe Movement of Agricultural Equipment on the Roadway.  It includes a section on Safety and a section called Farm Vehicles & Equipment And The Highway Traffic Act.  The manual is out-of-print, but is available for download as a pdf at http://www.farmsafety.ca/pages/manuals.html.  Slow internet connection?  Beware – it’s 60 pages (1.8 MB).

The section called Farm Vehicles & Equipment And The Highway Traffic Act is also available as a stand-alone document (html) at http://www.mto.gov.on.ca/english/pubs/farm/farm.htm.  It can also be downloaded as a pdf (35 pages, 405 KB).

Questions?  Comments?

Give me a call at (519) 674-1699 or email janice.leboeuf@ontario.ca.