"The history of every Nation is eventually written in the way in which it cares for its soil."
- Franklin D Roosevelt. Signing the Soil Conservation and Domestic Allotment Act.
  You are here:  PublicationsPest ReportsPest Reports - 2010   
 MOFGA's 2010 Pest Reports - Compiled by Eric Sideman, PhD Minimize

September 22 | August 23 | August 9 | July 26 | July 20 - Late Blight Update | July 19 - Late Blight Is Here | July 7 | June 24 | June 19 - Late Blight Update | June 18 | June 8 | May 25 | May 20 | May 3 | April 22
Show as single page
Pest Report - July 7, 2010

WHITE ROT OF GARLIC (Sclerotium cepivorum): It is only a month or so before it is time to harvest the garlic and growers should be aware of any diseases they have because a sure way to infect next year's crop is to use diseased seed. Of all the problems white rot is the most horrible. It is a horrible problem because it may spread fast, and once in a field it can take many, many years to get rid of. Inspect your crop now, and inspect your crop when you harvest it. Do not use or sell or buy any infected seed. If you have white rot, then you should not grow garlic in that field for many, many years.

White rot is one of the most destructive fungal diseases that affect the onion family. It is only a problem in the onion family. [It is not the same pathogen as white mold, which attacks many other crops such as beans, carrots, lettuce, tomato, pepper and more]. Symptoms of white rot on the leaves include premature yellowing and dying of the older leaves and then death of the plant. That is not much different than many other garlic problems, but the white, fluffy fungal growth (mycelia) on the root end of the bulb is the give away. Eventually this fungal growth moves around the bulb and inward between the storage leaves of onion and cloves of garlic. Small, black sclerotia (tiny hard, black bodies of dormant mycelia) form in the decaying tissue and throughout the white fluffy mycelia. Secondary infections by other fungi may occur.

There are no known spores. This fungus reproduces only by the sclerotia, and it spreads by direct contact. The sclerotia can lie dormant in the soil for many years until roots of a host plant grows nearby and the sclerotia are stimulated to germinate. Germination is optimum between 57 and 64 degrees and fungus growth optimum in soil is in the mid 70s with good soil moisture, but growth slows with warmer temperatures. The fungal growth spreads away from the infected plant and if it makes contact with a new plant it infects that one. So, the disease quickly spreads down rows of onions and garlic. Restricted areas of a field may be effected and other areas not. That is, until you drag the pathogen around on your boots or tiller or other equipment, or it flows with soil in heavy rains.

The pathogen spreads commonly by movement of infested soil on equipment and boots and by planting infected garlic seed, onion sets and transplants. Animals feeding on diseased bulbs can defecate viable sclerotia.

I have come across an interesting idea for speeding up the eradication of white rot sclerotia from the soil. Remember that the sclerotia will sit waiting in the soil for 20 or more years until a signal is received that onions or garlic are growing nearby. The growing allium releases a chemical that the sclerotia can sense. Over the past decade or so researchers have been playing with this knowledge trying to come up with a system that gets the sclerotia to germinate but, of course, have no alliums growing for the pathogen to complete its life cycle, thus reducing the number of sclerotia. I don't have a specific recommendation but a few things I have heard about that can reduce sclerotia in the soil include: 1) growing scallions which stimulate the sclerotia but are harvested before the disease spreads and new sclerotia are formed, 2) making compost out of onion waste and spreading that in the spring or fall repeated for a bunch of years before trying to grow an allium again, 3) making a concoction from ground up onion or garlic waste, or using garlic powder as a soil amendment for a few years before trying to go back to an allium. I wish I had a solid recommendation, but science is slow and this is a very complex problem. For now, pay attention to the stuff below.

Disinfectant Guidelines to Prevent the Spread of White Rot: The fungus that causes white rot is capable of surviving for many years as dry sclerotia on the surfaces of storage crates and bins and on harvesting and tillage equipment. In order that the fungus is not spread MOFGA recommends that all surfaces that may have been in contact with the disease, including boots, be sanitized with an appropriate disinfectant. Seed producers should execute extra diligence and may want to regularly disinfect any surface in contact with garlic.

Equipment, storage bins, etc should be effectively pressure-washed and then disinfested for ten minutes with sodium or calcium hypochlorite, (for example, 1:10 dilution of a household bleach such as Clorox, which is 5.25% NaOCl). Then rinse with potable water.

Since organic matter stuck on boots will inactivate chlorine materials, quaternary ammonium compounds may be used as boot dips inside storage areas and packing sheds, and before and after leaving fields. Quaternary should not be used on any apparatus that is in direct contact with the garlic or onions. Disposal of the dip solution must be in a manner that does not contaminate the soil, water or crop. Note: not all quaternary ammonium products are labeled for boot washes so read the label.

Best control is by good sanitation. Use clean seed for garlic and clean onion sets and transplants. If the infection is low, which is usually the case the first year it is found on a farm, pull the infected plants and destroy.

LATE BLIGHT UPDATE: At this time there is no late blight reported in northern New England. I am getting lots of emails and pictures of things that are not late blight and it is great to know that so many farmers and gardeners are being vigilant in their scouting.

The two most common culprits that are being thought of as a possible late blight symptom are blackleg (covered in the June 24, 2010 issue of the Pest Report), and feeding done by the tarnished plant bug (TPB).

Tarnished plant bug - note damage in upper right corner of picture. Photo by Eric Sideman.
The tarnished plant bugs, and other plant bugs, are rampant this year. I have never seen such numbers as in the clouds that rise out of my potatoes when disturbed.

Generally TPB is not a serious pest of potatoes. Even with the clouds this year the damage is minimal. But some leaflets are wilting and turning brown (see the picture in the web version of this report), and being mistaken for late blight.

The tarnished plant bug is a small (6 mm), bronze, brown and black bug that feeds on a very wide variety of plants. They overwinter as adults under debris and become active early in the spring. There are three or more generations per season. They are serious pests on strawberries (causing cat faced berries), lettuce (browning of midrib), flowers (destroying buds), eggplant and pepper (destroying buds), broccoli (brown beads in the head), and much more. But in potato they basically kill flowers (who cares?) and damage some of the leaflets (minor problem). It is pretty easy to kill them with pyrethrum, but not worth it because their numbers are so great in all the fields of hay and weeds surrounding you that what you kill will be replaced in a day or two. Weed and neighboring field management is about all you can do to keep the numbers low.

CATERPILLARS IN BRASSICA CROPS: There are three common caterpillars that feed on our broccoli family crops. Keep an eye out for them.

Quick ID Cues:

Diamondback moth caterpillar. Photo by Eric Sideman.
Diamondback moth caterpillar:
very wiggly when poked, pointed on both ends, not fuzzy, only grows to about 1/2 inch. You may find white silken cocoons, with a green full-grown caterpillar or a brown pupa inside. They eat wholes in the leaves.

Imported cabbageworm: gray-green, slightly fuzzy, and sluggish. Grows to >1 inch and favors the center of the head as it gets larger. Leaves wet green frass (droppings). Eggs single, light green or yellow. They eat large chunks out of leaves

Cabbage looper: light green, smooth, loops up like an inchworm as it moves, grows 1 1/2 to 2 inches. Eats big holes in leaves.

Scout undersides of leaves to look for fresh damage and notice and get control of caterpillars when they are small and damage is slight. Check heading crops as soon as heads start to form. Greens should be scouted at all growth stages.

For organic growers both Bt and Spinosad are very effective (Bt products are a lot cheaper), but remember to only spray after scouting and assessing damage. The pest has to be there to be killed, i.e., neither material has long efficacy after spraying.

Destroy crop after harvest so it does not act as a harbor for the pests all season.

MEASURING INSECTICIDES FOR BACKPACK SPRAYERS AND SMALL PLANTINGS: (Modified, short version of an article by Ruth Hazzard in the U Mass. Veg. Newsletter. For the complete article with examples go to http://www.umassvegetable.org/newsletters/current_news.html and look at the June 17, 2010 issue)
Growers with diverse crops and small plantings often need to be able to apply pesticide to beds or plots of several hundred square feet rather than acres, and the pesticide labels often only give rates on per acre basis. It is important to use the correct amount of insecticide in your backpack sprayer when spraying a small area. Calibration and mixing require some basic math, as do a lot of aspects of farming! The methods for backpack sprayers and tractor sprayers are essentially the same. Figure out the area to be sprayed and how much pesticide is needed for that area. Measure the amount of water you need to cover a known area, using the same equipment and walking or driving speed that you will use when spraying. Then ‘do the math’ so that the insecticide and the water rates both match your target area. Why does it matter? Why do you need to be careful about these rates? 1. Effective control of the pest depends on correct rates. 2. You are legally responsible for following the label instructions. This is especially important when you are selling the crop to the public. 3. The safety of the applicator, workers and the public depends upon correct rates and using pesticides according to instructions on the label.

Read the label. Find and follow the following instructions: --Personal protective equipment (PPE) – what you must wear when mixing and spraying. --Agricultural Use Requirements – this tells what protective equipment you should wear. --Crops and pests listed. The pesticide MUST be labeled for the target crop. --Restricted Entry Interval (REI) – during this time, no one should work in the sprayed area unless they are wearing protective equipment. --Days to Harvest (DH) – how long you must wait after a spray before harvesting (note: days to harvest may be less than REI; it is not a misprint) --Rate per acre or concentration per gallon (for backpack sprayer) --Mixing instructions.

The label often uses inconvenient measures. Conversions are key to your calculations. Here are some conversion ratios: 16 dry oz (by wt) = 1 lb One ounce (dry weight) equals 28.45 grams. 32 fl oz = 1 qt. 128 fl oz = 1 gal Liquid measure in (fluid) ounces is already a volume so it is easier to measure. One fluid ounce equals 6 teaspoons (tsp) or 29.6 milliliters (ml). An inexpensive measuring device for ml can be found in the children’s medicine section of drug stores. 43560 sq ft = 1 acre.

Entrust, for example- Based on repeated samples, we have found that there is 1.7 gm per teaspoon (shaved level and tamped slightly). So for Entrust the recommendation is 1.3 grams (3/4 teaspoon) in 3 gallons of water for 1,000 sq. ft.

Ants girdling base of stem of Brussels sprouts seedling. Photo by Eric Sideman.
I used to consider ants my friend. They aerate the soil, play a big role in decomposition and recycle nutrients, and for the most part do little damage out in the fields.

But this year they have girdled my Brussels sprouts and broccoli, wiping out entire rows. In the past I have seen them take down pepper plants and beans too, but usually only small numbers of them in a field. I have been told by Frank Drummond and Ellie Groden that they are looking for water or trying to get rid of plants I may have placed on top of their nests. I wish they would move elsewhere.

SQUASH BUGS: (Modified from article in U Mass Veg. Newsletter by Andy Cavanagh) Squash bugs are serious pests of pumpkins and squash. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Large populations can cause partial wilting, and later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable. Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. They overwinter and search for egg laying sites in late spring-early summer.

Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch.

Wingless nymphs hatch from the eggs and are similar in appearance to adults, are whitish when small, with a brown head, and grayish white when larger.

Squash bug eggs. Photo by Eric Sideman.
Squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense.

In small plantings it is very important to scout for and squash the first adults that are appearing now.

In larger plantings clean cultivation, crop rotation and sprays for cucumber beetle generally control squash bugs.

Rotate cucurbit crops between fields as far apart as possible.

Neem products (AZA-Direct for example) have shown promise as a chemical control (see the Resource Guide to Organic Insect and Disease Management).

Pyganic 5.0 may work too. However, this is a tough pest to control with accepted organic materials.

Scout undersides of leaves for squash bug adults and eggs and get ready to treat if the copper-colored egg masses exceed one per plant.

Squash bug nymphs. Photo by Eric Sideman.
Time squash bug sprays to kill young nymphs, which are easiest to control.

Thorough coverage is necessary.

Treat very late in the day when the flowers are closed to reduce risk to bees.

Keep headlands mowed and free of trash to reduce overwintering sites.

Clean cultivation helps reduce populations, while use of mulches and reduced tillage favors squash bug survival.

Bugs favor certain winter squash (Hubbard or marrow) over other cucurbits. One way to control adult colonization of fields in the spring is by planting a perimeter trap crop (Hubbard or marrow) 1 or 2 weeks before the main crop, and treating the trap crop just prior to main crop emergence or prior to transplanting, and 5 to 10 days later.

July 19 - Late Blight Is Here | Page 7 of 15 | June 24


Home | Programs | Agricultural Services | The Fair | Certification | Events | Publications | Resources | Store | Support MOFGA | Contact | MOFGA.net | Search
  Copyright © 2014 Maine Organic Farmers and Gardeners Association   Terms Of Use  Privacy Statement    Site by Planet Maine