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Home  > Question of the Week

Question of the Week

Permalink Can I grow an orchard on north-facing slope?

Answer: The University of Wisconsin has written about this in the publication Planning and Establishing a Commercial Apple Orchard in Wisconsin. That publication states:

"The exposure of the slope is also important. South-facing slopes experience more temperature fluctuation during the winter than north-facing slopes. Winter injury to tree trunks can be caused when sunlight reflecting off of snow causes trunks to warm and to lose hardiness. Bright sunny days followed by bitter cold nights can injure trunks that have lost hardiness. With the low angle of the winter sun, north-facing slopes receive less sunlight."

In other words, a north slope is actually preferable. This is true for pears, apples, peaches, and cherries. There is even a type of damage to fruit trees dubbed "Southwest injury" because of the phenomenon described above.

Additionally, all other things being equal, the soils on north-facing slopes have higher average proportions of organic matter. That is simply because the heat favors the bacteria that breakdown organic matter. This can be a very important factor in areas where soil organic matter is at a premium.

For the University of Wisconsin publication referenced above, see

For more information on orchard site selection, see the ATTRA publication Tree Fruits: Organic Production Overview, available at

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Permalink What is the best way to store cucurbits like zucchini and cucumbers for several days? Should they be refrigerated?

Answer: Contrary to common belief, washing zucchini or cucumbers prior to storage is not recommended. If the fruit is muddy, then wash it, but make sure it is completely dry before boxing it. If you pick squash and cucumbers that feel gritty, it is best not to wash them, as doing so could reduce the fruit's shelf life.

After the fruit is dry and boxed, deciding whether to refrigerate or not depends on what is going to happen with the fruit after it is boxed. Boxed squash or cucumbers should never be stored in the sun. The cardinal rule of post-harvest handling of fresh vegetables is that once they are off the vine or the plant, they should never be exposed to the sun again.

If you are going to be selling the fruit yourself at an open-air farmers market, you should put it into an air conditioned room, rather than refrigerate it, if that is possible. If you can get the temperature of the fruit to drop to less than 80 degrees F overnight, it will last much longer.

If you are going to sell the fruit to a retail grocery store or to a local wholesaler, then you should refrigerate the boxes as soon as possible. If you will be delivering the fruit from your place of business to the retail store or to the local wholesaler in a refrigerated truck, then you should store the boxes at 50 to 55 degrees F. If you will be delivering the fruit in an unrefrigerated vehicle, you should only cool the fruit down to about 65 degrees F. Avoid cooling the fruit way down to 50 to 55 degrees and then delivering it in an unrefrigerated vehicle. This dramatic swing in the internal temperature of the fruit is not good. Under no circumstance should you put summer squash or cucumbers in a cooler that is less than 50 degrees F.

To learn more, read "Harvest/Post-Harvest Handling and Food Safety – Field Exercise," from the Western SARE Farm Internship Curriculum and Handbook. It is available on the ATTRA website at

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Permalink How do I control mosquitoes in my rice paddy?

Answer: There are several non-chemical options available. Commercial formulations of Bacillus thuringiensis var israelensis (also known as "Bti") are available in pellet or powder form that can be applied to rice paddy water. The Bti product is made up of the dormant spore form of this naturally occurring soil bacterium, as well as an associated pure toxin. The toxin disrupts the gut in the mosquito by binding to receptor cells present in insects, but not in mammals. Another form of Bti is available as a product called Mosquito Dunks. One donut-shaped dunk can control mosquito larvae in a volume of 100 square feet of water for 30 days. Please be aware that Bti is also lethal to a wide range of filter feeding insect larvae, including gnats.

Another option is to put "mosquito fish" (gambusia) into the rice paddy. These fish eat mosquito larvae. Several counties in California distribute mosquito fish at no charge to residents with man-made fishponds and pools as part of their Mosquito Abatement programs. However, it is not recommended to introduce them into natural habitats (streams, lakes, etc.), because these introduced species compete with native species.

A third option is to remove all the water periodically. Water in rice is primarily used as weed control, as the water drowns most weeds, which are not as efficient as rice is in transporting oxygen to the roots. Periodic removal of water will allow the paddy to dry out, killing the larvae, or at least reducing their populations.

See for ATTRA's ecological pest management database and sourcing information for the above-mentioned biorationals.

Further Resources:

Managing Mosquitoes on the Farm, UC Mosquito Research Program
This site has much information about managing mosquitoes in an agricultural setting, including rice paddies.

Pesticides and Public Health: Integrated Methods of Mosquito Management, Center for Disease Control
This article reviews various approaches to mosquito control, including biological.

Florida Mosquito Control Association
This site has links to dozens of other mosquito sites across the country, and abatement districts in both Florida and California.

The mention of specific brand names does not constitute an endorsement by NCAT, ATTRA, or USDA.

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Permalink What could be causing the heads of my young white cauliflower to turn yellowish-brown?

Answer: Yellowing or browning of white cauliflower heads can be attributed to frost damage, sun damage, or boron-deficient soil.

Cauliflower is a cool-season plant belonging to the Brassica family. However, it can be damaged if the temperatures are too low or if exposed to a hard freeze. If you have experienced extremely cold night temperatures, this may be the reason for discoloration.

If you have ruled out frost, are you blanching your cauliflower heads? Blanching involves pulling the leaves up over the head of the cauliflower to shade it which ensures the cauliflower head remains a crisp, white color. The leaves can be tied together but this makes it easy for water to collect, which could rot the head of the cauliflower. A safer bet is to bend the larger outside leaves over the crown and loosely tuck the edges to hold it in place, which allows for proper air circulation. Some varieties of cauliflower are even “self-blanching.”

If you have not experienced a hard freeze and you have been blanching the cauliflower heads, it is likely your problem is boron-deficient soil. This will cause the heads to turn brown and leaf tips to curl or become distorted. A soil sample could help determine if your soil is deficient. However, since the uptake of boron by the plant depends on different factors, such as the percent of organic matter in the soil, moisture levels, and the pH, a soil test that indicated sufficient boron levels would not eliminate the possibility of a boron deficiency.

Boron is one of seven essential trace minerals that plants need in very small amounts to grow well. Cole crops need higher amounts than other crops. It's easy to over-apply boron in trying to rectify a deficiency. Consider looking at other factors like soil moisture levels, good pH levels, and organic matter content of the soil before applying boron. If it has been dry, keeping the soil moist with irrigation may help the uptake of boron. Fixing the pH and building organic matter are both longer-term solutions that will help with future plantings. For subsequent crops, provide boron by adding compost to the soil, or plant fall cover crops of vetch or clover. A foliar feeding with kelp or fish emulsion could help, as these both are high in boron. If you decide to apply boron it's recommended at a rate of only .1 to .25 lb/acre as a foliar spray. The amount used depends on the percentage of boron in the product you are using.

For more information about growing cauliflower, refer to the ATTRA publication Cole Crops and Other Brassicas: Organic Production, available at

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Permalink What are the best organic methods for dealing with a blister beetle infestation?

Answer: For many market farmers, blister beetles can wreak havoc on crops in a very short time. The beetles seem to prefer tomatoes, potatoes, and chard, but easily move on to peppers and eggplants. More importantly, they infest hay and are poisonous to animals feeding on the hay, even if the beetles are no longer alive, due to the presence of a toxic chemical in their bodies called cantharidin. Handling the adults should be avoided, as cantharidin can irritate or blister skin on contact. If handled gently, this may not be a problem.

Populations tend to appear suddenly in June and July and usually will feed together in groups. Blister beetles usually overwinter as last-stage larvae and prey on either grasshopper eggs or bee eggs, so keeping grasshopper populations low is necessary to effectively reduce blister beetle populations. If grasshopper populations are high one year, there is increased likelihood that the following year will see higher than normal blister beetle populations.

Some effective options to control the adults are pyrethrum, a broad-spectrum botanical insecticide, and a kaolin clay product sold under the brand-name Surround. Surround is not directly toxic to the beetles but acts in two ways: it changes the color of the plant, thereby confusing the insect, and it also causes most insects that land on a kaolin clay-coated plant to spend much time grooming themselves to remove the clay particles. This reduces the time they spend feeding. Keep in mind that many plants can withstand considerable defoliation before there is a decrease in yield. Neem-based products (containing Azadirachtin) have also reportedly been effective against blister beetles, though if you have a large infestation of blister beetles, you might consider using a formulation of spinosad.

Other management strategies include early planting and harvest of crops to avoid the June/July peak blister beetle season. Row covers are also an option, but you must be sure that no beetles will emerge beneath (inside) the row covers. If your plot is relatively small, then the beetles, which tend to congregate in one area, can be knocked into a bucket of soapy water, which will kill them. Using a preferred crop or even a preferred wild host like passion vine as a trap crop is also an option; the trap crop can then be treated for the beetles. Lastly, creating environments attractive to blister beetle predators, including robber flies and birds such as meadowlark, bluebird, and scissor-tailed flycatcher, can help reduce the population.

See for ATTRA’s ecological pest management database and sourcing information for the above-mentioned biorationals.

For more information, see the following ATTRA publications:

Biointensive Integrated Pest Management

Farmscaping to Enhance Biological Control

Grasshopper Management

The mention of specific brand names does not constitute an endorsement by ATTRA, NCAT, or USDA.

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