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 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
 
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Remember, the pest report often has pictures but to view them you need to go to the MOFGA website (mofga.org) and under publications you will find the Pest Reports.

ASPARAGUS (Modified from UMass. Veg. Newsletter)

Frost: One of the very first questions I received when I began working for MOFGA many, many years ago turned into an argument. Not a good start, huh?. The guy who called would not believe me that asparagus is frost sensitive. His spears had turned dark, wrinkled and water-soaked and I don't know if I ever convinced him. Perhaps he is reading this.

Asparagus, despite its status as a primo early season vegetable, is highly sensitive to frost, ranking alongside cucumber, snap beans, eggplant and tomatoes in the ‘most susceptible’ category. The early hot spell this year moved everything, including asparagus, ahead by weeks. It made some growers in-the-know uneasy as spears pushed out of the ground, only to face the a string of cold nights and snow. There is still a good chance of frost though you would not believe it since it was near 90 yesterday!

When frosted, spears appear slightly darker green, water-soaked and break off easily. Thawed spears become mushy. Soft-rotting bacteria can enter the damaged tissue. New spears take several more days to emerge, but will. Temperatures below 33 degrees Fahrenheit may damage the spears.

Asparagus beetle eggs. Photo by Eric Sideman.
Beetles
: Common asparagus beetles tend to arrive in mid May (I bet this year earlier). The spotted asparagus beetle generally becomes active somewhat later in the spring, and in my experience is less common (I guess with the names that is not a surprise). These two beetles are closely related and have similar life cycles but it is the common asparagus beetle that is most damaging to the cut spears.

Common asparagus beetle (Crioceris asparigi) is blue-black, shiny, smooth and about 6 to 9 mm (1/4 inch) long, with three large yellow, squarish spots with red margins along each wing cover. Eggs are black, laid standing on end in rows along the spears, and hatch in 3-8 days. Larvae are wrinkled, plump, hump-backed, and dull gray with black head and legs. They grow up to 1/3 inch. These larvae feed in spears and in ferns. The larvae do the most damage, and eggs and larval damage makes spears unmarketable. Larval feeding can cause severe defoliation and weaken the stand. When full grown, larvae drop to the soil and pupate underground. New adults emerge in July, feed in ferns, and by September are looking for overwintering sites.

Spotted asparagus beetle (Crioceris duodecimpunctata) is reddish orange or tan, with six black spots on each wing cover (hence its other name, 12-spotted asparagus beetle). Eggs are greenish, glued singly on their sides to leaves. Eggs are laid on fronds, not on spears. Larvae are similar to those described above, but are orange colored, and feed almost entirely inside the berries so they affect seed production but do not hurt the plants.

Asparagus beetle larva.
Photo by North Carolina Cooperative Extension.
Winter habitat: Both species spend the winter as adult beetles either in field borders or within the asparagus field. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil.

Scouting: Early in the season, look for adult beetles, for feeding damage and for eggs laid on spears. Michigan State recommends a treatment threshold of 5-10% of the plants infested or 1-2% of the spears with eggs or damage.

Cultural controls: During harvest, you can greatly reduce the population by harvesting ALL of the spears every day.
Pick the field clean to reduce the number of stems where eggs will survive long enough to hatch or larvae can feed and grow up into summer-generation beetles. In the fall remove all of the crop residue and other refuse nearby that may provide shelter for adults over winter, by disking lightly (avoid crown damage) or burning crop stalks and fronds. Maintaining a clean environment in the fall will force beetles to seek shelter outside the field or burrow in the soil, where many predators reside.

Asparagus beetles. Photo by Eric Sideman.
Biocontrol: The most important natural enemy of Common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. Wasps kill eggs by feeding on them (sucking them dry), and also lay their own eggs
inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs killed by feeding and half of the surviving larvae parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.

Monitoring and chemical control: Scout fields regularly. You may want to treat spears if >10% of the plants are infested with beetles or 2% have eggs or damage. The daily harvest makes treatment difficult because few want to spray anything close to harvest time. Organic options on spears include Surround WP as a repellent, Pyganic EC5.0, or Entrust.

R Hazzard. References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell University


SEEDLING PROBLEMS

Raising seedlings in a "sterile" mix such as Pro Mix is easy. These mixes are called sterile, however they are not really sterile. On the other hand they are called sterile by growers because they don't have plant pathogens in them, and that beats my home-made mix. These "sterile" mixes are mixes of pathogen free materials such as peat, perlite, vermiculite with synthetic and very available sources of plant nutrients added in just the right amount to get newly germinated plants off and growing. Organic growers do not have the option to use these mixes. We either purchase mixes that are generally based on compost, or mix up our own. Seedling problems are much more likely in organic mixes because of the possibility that the compost may be carrying plant pathogens. In addition, it is much more difficult to predict the availability of nutrients from natural sources because of how biological activity is greatly affected by temperature, moisture and other factors. Many commercially available organic mixes are quite good and consistently free of pathogens, and good with nutrients, but occasionally even these fail. Home made mixes, such as the one I make, fail more regularly. Here are some of the problems I have seen frequently in my home made mix, and occasionally in commercial mixes.

Damping-off: Damping-off is a disease most commonly seen in young seedling but may rarely effect older seedlings. It is caused by species of fungi that commonly live in the upper layers of soil and when things are not right these pathogens jump at the opportunity to infect germinating seeds and seedlings. The two most common species that cause damping off are in the genera Pythium and Rhizoctonia.

There are two types of damping off. The first is one growers often misinterpret because it is pre-emergence damping-off, which rots the sprouting seed before it breaks through the soil. Growers often blame the seed companies for poor seed. The fungus attacks any part of the germinating seed especially the tiny growing tip. Post-emergence damping-off begins as a lesion on the root which extends up the stem to and/or above the soil line. The young stem is constricted by the attack and becomes soft, and the plant falls over and dies.

Damping off cannot be cured but it can be prevented by starting seeds in better conditions (or the "sterile" media). First make sure you are using seeds of the highest quality. Old, mistreated, and weak seeds are more susceptible to damping-off. Anything that slows germination increases the risk of infection. Excessive watering, poor drainage and less then optimum temperatures should be avoided. Allow the surface of the container to dry a bit before watering.

It is possible to "sterilize" your media by baking the mix in the oven at 350 F for about 45 minutes. The mix should reach 1600 and should stay at that temperature for 30 minutes. Do not allow it to go higher or stay hot longer because overheating kills the beneficial microorganisms and may releases toxic materials

Cold Soil/Wet Soil: In addition to damping off, cold soil can cause other problems. Growing seedlings on window sills is often a problem because of cold night time temperatures. The roots of plants do not function when cold and plants frequently display symptoms of malnutrition even thought the media may have plenty in it. Purple undersides of leaves, stunted growth, pale weak seedlings are often the results of cold feet or wet feet. Trying to grow a tiny seedling in a large container may have the same effect because the plant is just not big enough to use the water and over watering may be a problem the plant cannot get out of.

Salt: Some composts are high in soluble salts. Even if the salts are nutrient salts such as nitrates, high salts will cause water absorption problems and may prevent seeds from germinating. Salty composts are not a problem in field use because they become diluted with the soil, but in a seedling media it is a real problem. Compost used for media should be the best you can get and should not have salts -measured as conductivity on a compost analysis- higher than 1mmhos.

Carbon:Nitrogen: The C:N ratio is critical for compost used in potting mixes. A high C:N ratio will result in nitrogen lock up, which is a case where all the nitrogen in the media, and any you add with fertilizers, is being grabbed by the bacteria feeding on the carbonaceous material. It is a sign that the compost was made from an improper mix of feedstock, or perhaps is just not finished yet. Compost used to make media should have a C:N ratio of 15:1 to 18:1.

Ammonia: As nitrogen is released from decomposing proteins in a compost pile it passes through a phase where it is an ammonium ion. Unfinished compost will have ammonium ions that may revert to ammonia and kill roots. Ammonia nitrogen in a compost used for a potting soil should be less than 0.1%. Problems from high ammonia can be seen as very weak, dying seedlings, and when you pull them up you see that the roots are brown instead of a nice healthy white.

My recommendation is to get an analysis of any compost you plan to use to build your own seedling mix. The University of Maine Soil Testing Laboratory does compost testing. Just be sure if you send a sample to ask for the compost analysis. If you are buying a commercial compost based mix you may want to speak to other growers and see how that brand has worked for them.


DAMPING-OFF IN THE FIELD

Above I discussed damping-off of seedlings. Last year I received calls about peas dying just after or just before germinating and I thought I better say that damping off can occur in the field too. This time of year the problem is with peas.

The disease is caused by several different species of Pythium, which is a common soil inhabitant that persists in soil in root debris as spores. The species have a wide host range of crops and weeds and so crop rotation will do little to avoid the problem.

During or just after germination the pea seedling begins to show symptoms. The symptoms may be as simple as yellowing and stunting because sometimes only the root tips are infected and this root pruning interrupts growth. Sometimes a soft rot of the stem kills the plant. Sometimes you just don't see any pea germinate.

High soil moisture and warm soil temperatures (warmer than optimum for pea growth, i.e., 65-75) favors Pythium. You can't control the weather but you can choose when you plant your peas. If the soil is very wet and warm weather is forecast it may make sense to delay planting a few days for the soil to dry a bit.

There are resistant varieties. The resistant gene is tied to some visual characteristics of the seed. Wrinkled seeds are more severely affected than round seeds. Also, some biological seed treatments such as Rootshield may help.


POTATO PLANTING TIME: DON'T PLANT A PROBLEM

Late blight on tubers. Photo by Eric Sideman.
Potato seed tubers are often the source of infection for your crop and inspection before planting is well worth the time. Some problem seed pieces are not going to spread a disease and can be planted. Others should never be planted. Here are some common issues:

Late Blight: Of course this is the big one. Look at the picture on the web version if you don't know what this looks like. If you are not sure, check with an expert. Besides taking down your potato crop, this is the most likely source of a community or state wide problem this year. Do not plant any potatoes suspected of being infected with late blight.

Fusarium Dry Rot: This is probably the greatest cause of loss in storage. It is also seen on seed pieces, and can result to seed piece decay after planting and result in uneven stands. A slimy rot ofen develops when Fusarium dry rotted potato seed is planted. This is a secondary infection by bacteria, which take over. Do not plant seed pieces with Fusarium dry rot.

Ring Rot: This is one of the worst diseases you can get on your farm because once you get it it is very hard to get the farm clean again, and it spreads very easily by the bacteria clinging to boots, crates, and equipment. Check your seed carefully and discard the whole load if any ring rot is found. In the tuber you will see the disease as a break down of the ring of vascular tissue when you cut the potato. Squeezing the tuber will expel creamy, odorless ooze of bacteria. Planting these tubers will introduce the bacteria to your soil.

Scab: Lesions on the tuber are usually circular and seldom larger than a half inch, but in very bad infections they coalesce. They may be a cork like layer or pitted. The layer under the lesion is straw colored. Planting these tubers will introduce the bacteria to your soil.

Black Scurf: If you have little black, irregular lumps on the skin of your potatoes that resemble soil but will not wash off, then you have black scurf. This is a disease that is caused by a fungus called Rhizoctonia solani. The black specks are one of the ways the fungus reproduces. They are called sclerotia, which are tight, dry masses of fungal tissue (mycelium) in a resting phase. In the spring the sclerotia germinate and infection of the new potatoes begins. Most commonly, infection of potatoes is from planting potato seed pieces with sclerotia on them. Crop rotation is not very effective because sclerotia can survive for many years without a host crop. So, avoid ever planting seed with the disease.

Hollow Heart: Just as the name implies, the center of the potato is hollow. It appears as splitting with the tuber and the inner walls may be white, tan or even may be rarely infected with a secondary disease. Hollow heart is not caused by a pathogen but rather by rapid tuber enlargement especially after a period of moisture stress. Potato seed with hollow heart will not spread the disease.

Knobby potatoes: Potatoes with knobs are usually the result of high field temperature and drought or other conditions that cause irregular rates of tuber development. Planting knobby potato seed will not spread the problem.

May 20 | Page 14 of 15 | April 22

    

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