Diseases and Insects

There is a wonderful reference to plant pests organized by plant variety on the website of the Connecticut Agricultural Experimental Station.

Initially, I thought I would record all disease and insect damage for all cultivars, but often there are multiple infections, and accurate identification is difficult Since this method has proved to be too time consuming, I will evaluate grape cultivars primarily on whether they produce a good crop of grapes - after all that is the bottom line. 

Below are a few of the most common grape issues seen here in Connecticut.

There is a wonderful pocket guide from Michigan State University full of color photos to help you identify all grape issues that include diseases, insects, animals, nutritional deficiencies, and chemical injury, "A Pocket Guide for Grape IPM Scouting of Grapes in North Central & Eastern USA"  

Three conditions need to be met for disease to manifest in plants - this is called the "Disease Triangle":

• Susceptible Plant
• Pathogen
• Favorable Environment

Eliminate any one of these three and there is no disease.

The strategy of this grape trial is to address all three of these conditions, that is:

• Eliminate the most susceptible grape varieties.
• Reduce pathogen levels with dormant spray over the Winter.
• Provide good air flow through the leaves while maintaining good sanitation in the vineyard by policing debris and dead leaves.

Diseases

Organic Dormant Sprays During the Winter

The goal of dormant sprays is to eliminate fungal pathogens that overwinter in or on the woody parts of the vine. While it is not possible to eradicate all inoculum, dormant sprays can kill or debilitate the fungus resulting in fewer spores, thereby reducing disease pressure during the growing season. 

Generally, a 30 to 50 percent reduction in disease pressure can be expected from a single dormant spraying. Dormant sprays are useful for management of anthracnose, black rot, mildews, and phomopsis. 

There are several types of dormant sprays permissible for organic growing:

• Horticultural Oil
• Copper Octanoate
• Bordeaux Mix (Copper Sulfate + Lime)
• Lime Sulfur (Calcium Polysulfide) 

The first one is a harmless mineral oil. The other three are hazardous so, if used, understand and religiously follow the directions for safety.

Three applications are recommended, weather permitting.  The approximate application dates should be: Thanksgiving, New Year's Day, and Valentine's Day - allowing at least one month between different types of sprays. Spray when temperatures are above freezing, winds are low, and rain or snow is not expected for at least 24 hours. Protect yourself with masks, eye protection, and proper clothing per directions on each product.
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Anthracnose

​Notice the typical ‘bird’s eye’ infection on the grapes. Leaves may curl and distort like a clenched fist. Lesions appear on stems.

Anthracnose is caused by a fungus. The disease is of European origin; therefore, Anthracnose is generally worse on American grapes. Sanitation is extremely important. Remove old, infected plant material, which is the primary source of spores for new infections.

Organic growers can be selective about which cultivars to plant and apply organically approved lime-sulfur sprays during the dormant season – this fungicide helps to reduce the amount of primary inoculum.

​Subsequent fungicide sprays from bud break to veraison (color change of grapes) may be necessary every 10 to 14 days where Anthracnose is severe. Caution: some cultivars are sensitive to sulfur – see widely available charts.

If you want to avoid sprays (other than dormant sprays), as I do, choose cultivars that are resistant to Anthracnose.

Black Rot

Notice the round orange-brown circles on the leaves and the damage to the grapes. Also notice the typical black ‘mummy’ grape in the lower foreground of the right photo. To the left of it is a grape in the earlier stages of becoming a ‘mummy’. Some cultivars are more susceptible to Black Rot than others.

Organically approved fungicides (copper and sulfur) are not very effective for Black rot control. So, the most efficient way to control Black Rot is the use of good cultural practices. Avoid susceptible cultivars. Also, sanitation is a key component to controlling Black Rot. Clear all mummies from the ground after leaf drop or till them into the soil prior to bud break. Remove all mummies from the vines during dormant pruning.

Photo Phomopsis Cane and Leaf Spot

Notice the lesions on the canes and leaf, and the rotting of the berries. Although infection starts in the Spring, Phomopsis symptoms appear at harvest, whereas black rot symptoms usually appear before harvest. 

Sanitation is crucial to eliminate the primary source of spores for new infections, which are found on disease portions of the plant. Removing infected canes during dormant pruning and destroying canes, clusters, and other plant parts can significantly reduce the number of spores. Also, good airflow can help keep leaves and canes drier.

Botrytis Bunch Rot

Tight clusters are more prone to Botrytis than loose clusters. It usually does not become apparent until the berries start to ripen, when it is too late to reverse. Sun, good air flow, and sanitation help control it. Also, selecting varieties resistant to this disease.

Powdery Mildew

Powdery mildew fungus does not require free water on the plant surface to infect. In can grow in even low humidity environments. Powdery mildew can result in reduced vine growth, yield, fruit quality, and winter hardiness. Varieties of vinifera and its hybrids generally are much more susceptible than American varieties.

Downy Mildew

Downy mildew is a major disease of grapes throughout the eastern United States. The fungus can rot berries, clusters, and shoots and cause premature defoliation of vines. This premature defoliation is a serious problem because it predisposes the vine to winter injury. It may take a vineyard several years to fully recover after severe winter injury.

Controlling Downy and Powdery Mildew

Researchers have found milk, baking soda, and oil to be just as effective as fungicides in controlling the mildews. We tried it and it works. It is best to catch it early. If you wait too long, it is too late. It works on grape, squash, and cucumber leaves. Spray weekly during the mildew season (Aug-Sept).

Ingredients:

• 2 cups non-fat organic milk*  (for Downy Mildew)
• 1 TBS Baking Soda (for Powdery Mildew)
• 1 TBS of any cooking oil (for Powdery Mildew)
• 1 TBS dishwashing liquid (for Powdery Mildew)
• 8 cups water
• TOTAL 10 cups

* If there is milk fat in the milk, it will smell after sitting on the leaves in the sun. That is why non-fat milk is suggested. Caution, spray when bees are not present (non-sunny days, either early or late in the day). Otherwise, the oil and soap will act as an insecticide and kill them.

Insects

There are several things that can be done to control insects organically. Healthy soil and plants is a good start.  Bugs are more likely to attack unhealthy plants on poor soil. A large variety of different species of plants will help, as well, by balancing good and bad insects. With this information as a basis, here are some additional specific measures that can also be taken.

Asian Fruit Fly (SWD - Spotted Wing Drosophila)

In the past two years, this invasive species has become the biggest issue on our site for our grape and fruit crops.

In 2020, to try and control the Asian fruit flies, we are going to use paper bags to enclose and protect grape bunches. Also, we will use insecticidal soap. If these measures are not effective, only then might we resort to Spinosad and Pyrethrin which are two insecticides that are effective against SWD and approved for organic production.  I will report our results the following winter.

Unlike the native fruit flies, which only attack rotten fruit, the SWD attacks good fruit by laying eggs in the fruit which then feeds the growing larvae. 

SWD grows from egg to adult in as little as 10 days. The short development period means there can be as many as 13 generations in a single growing season. These nasty invaders number in the thousands and seem to prefer some grape varieties more than others.

SWD is known to infest many cultivated and wild fruits including apricot, blackberry, blueberry, buck-thorn, cherry, cranberry, currant, dogwood, fig, grape, kiwi, peach, plum, raspberry, and strawberry. Such a wide variety of host crops makes it difficult to control.

I experimented with plastic bags over the grape bunches to see if they protect from disease and the Asian spotted wing drosophila (SWD). 

Plastic bags work great on apples and pears, so I wanted to see their effect on grapes. They were ineffective. The tiny fruit flies entered through the small rain vent holes at the bottom of the plastic bags and infest the grape berries.

Japanese Beetle

Japanese Beetles can decimate your grape leaves. Fortunately, there is a great organic solution and is safe to use - Milky Spore. This powder is available at your local Agway. One 20-pound bag treats 7,000 square feet. Spread it according to directions on your entire growing area in the Spring, Summer and Fall for two years, then repeat every ten years. This harmless (to humans and animals) bacteria kills Japanese Beetle grubs overwintering in the ground. On our site, it has reduced the Japanese beetle populations 100-fold from thousands down to dozens - effectively minimizing this threat.

Any adult Japanese Beetle stragglers that survive can be collected by dropping them in a mason jar 1/4 filled with wine. They are easy to scoop from the leaves to the jar.

Phylloxera

Grape Phylloxera is a microscopic aphid-like louse that lives on and eats sap in grape leaves and roots. The foliar form overwinters as eggs on canes. The use of dormant oil can help kill these. Eggs hatch when the leaves emerge in the spring. Nymphs move to upper leaf surfaces and begin feeding. Their feeding induces the formation of galls on the leaves. After about 15 days, the adult stage is reached within the galls. At this rate of maturation, 6-7 generations occur on the leaves within one season. 

Crawlers will move from older leaves to more tender leaves at shoot tips.

There are no good controls for Grape Phylloxera other than the application of dormant oil, avoiding susceptible cultivars, and using Phylloxera-resistant rootstock grafts for susceptible cultivars. On vinifera, they are devastating. On American and hybrids, they are unsightly but are not usually a significant threat to the grape production.

Row Covers

This is one of our primary methods of insect control for certain crops. It prevents insects from laying eggs on baby greens, so the plants grow healthy and mostly bug free. Without row covers, greens can become heavily infested. With row covers, we usually get a good crop.

Row Covers are needed for greens, cabbage, and young eggplant. Row Covers are not needed for peppers, tomatoes, squash, and cucumbers. 

The hoops are made from 1/2" Poly Pipe for $20 per 100' roll. Cut off lengths to form the half-hoops. - Then stick the ends into the ground for support. 

The fabric we use is Agribon+ AG-19 83" x 250' for $37 from Johnny Seeds. One roll lasts many years.

​We use short pieces of rebar to hold down the fabric.

Bug Jars

To handle most insect issue not controlled by row covers, we do a daily walk with mason jars 1/4th filled with wine. We pick and drop harmful insects into the wine. This is mostly for squash bugs, potato beetles, and caterpillars in the veggie and berry gardens. This reduces their numbers and the damage.

Insecticidal Soap

Occasionally some harmful insect population can arise, and we spray with insecticidal soap for these.

Ingredients:

• 1 TSB of liquid soap
• 1.5 tsp of any cooking oil
• 1 quart of water.

This solution only works when you spray the insects directly. There is no residual effect. Do not spray when bees are flying so as not to harm the bees. Some years we need this occasionally. Other years we do not need it at all.

You can add garlic, onions, and cayenne pepper for a residual effect - the odor and discomfort keeps the insect away. But do not spray these where you need bees for pollination - it will scare them away also and you will get no fruit.

Lyme Disease

Unfortunately, you need to be concerned with more than just grape diseases. Ticks host a number of diseases transmissible to humans. 

Besides Lyme Disease ticks can transmit:
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• Anaplasmosis
• Babesiosis
• Borrelia mayonii
• Borrelia miyamotoi
• Bourbon virus
• Colorado Tick Fever
• Ehrlichiosis
• Heartland virus
• Powassan virus
• Red Meat Allergy (Alpha-Gal Allergy)
• Rickettsia parkeri rickettsiosis
• Rocky Mountain Spotted Fever
• STARI (Southern tick-associated rash illness)
• Tick-borne relapsing fever (TBRF)
• Tick Paralysis
• Tularemia
• 364D rickettsiosis 

Lyme Disease, Babesiosis, Anaplasmosis, and Ehrlichiosis are the most common.

In the Summer of 2019, I wound up in the hospital with fever and cellulitis near my ankle - doctors surmised this broke out from Lyme Disease (confirmed by blood test) that triggered this infection. A month earlier, I found a tick deeply embedded in my back which we removed. However, in the past 40 years I have experienced over 100 tick bites, most without incident.

Apparently, you can break out with cellulitis in an unbitten area from Lyme Disease. I was not bitten on the ankle and there was no break in my skin initially at my ankle.

The infection spread very rapidly. Late afternoon I had a little itching on my ankle. The next morning a red area the size of a quarter appeared. By evening it was too painful to walk on that leg so we went to the hospital, and was put on intravenous antibiotics initially, followed up by oral antibiotics for three weeks, it healed up fine.  Normally I am quite healthy with good resistance, but stuff happens.

There are many sprays you can buy to discourage or kill ticks. 

I prefer to use netting like those available from BugBaffler. Since I have found ticks crawling up my legs and arms, I use these same nets for my legs and arms. The white color allows you to easily see the ticks. 

Also, we do daily full-body tick checks whenever we venture outside - ticks are also active in the Winter, so you need to check year-round.