Remember to Supply Calcium for Blueberries

Blueberries are members of the Heath family, which includes azaleas, camellias and rhododendrons. These are acid-loving plants which thrive on a low soil pH. Blueberries like a soil pH between 4.5 – 5.0. In order to lower the soil pH, elemental sulfur (97% sulfur) is added. This is best done at least one year before planting to allow the sulfur to react with the soil and lower the pH.

I have seen newly planted blueberry fields never attain good plant growth because the sulfur was not added to the soil until after the plants were planted. One field especially comes to mind: the grower added plenty of organic matter to the soil and put in drip irrigation, took soil samples and added the required fertilizer. But he neglected to bring down the soil pH. Soybeans were previously grown in the field and the pH was 6.5. Even though he desperately tried to get the pH down, the plant leaves turned pale and chlorotic.

During the summer, heavy rains washed out part of the field and uprooted several plants. The following year, he replanted the areas of the field that had missing plants. Those plants started to grow immediately and did not show any signs of plant stress or chlorosis – because the soil pH was brought down to 4.5 by the sulfur application one year earlier and the newly planted plants responded immediately to the ideal soil pH. This response was very dramatic and I always try to remind growers that the three most important things you need to have a successful blueberry planting are pH, pH and pH!

Calcium is a very important plant element that blueberries need in order to build good cell walls in the fruit to keep them firm. Usually, calcium is supplied to the plants by the application of calcium carbonate (limestone). However, limestone will raise the soil pH, which is not what we want for blueberries. So we get calcium into the blueberry plant by applying calcium sulfate, otherwise known as agricultural gypsum. (Do not confuse this with building supply gypsum that may contain binding agents or other non-plant nutrients.)

For young plants, apply two cups of gypsum around each plant in the row any time during the growing season. If you have plants that are older than 10 years, you can apply about a pound of gypsum around the outer periphery of the plant and water it into the soil. According to Charlie O’Dell, former horticulturist with Virginia Tech, “agricultural gypsum contains a neat balance of both calcium and sulfur so that it has no effect to alter soil pH up or down. Agricultural gypsum contains 32.5% calcium oxide, or roughly 25% actual calcium, so a pound of ag gypsum per plant replaces about four ounces of depleted calcium, and is quickly available to the plant roots. Ag gypsum also benefits soil structure by loosening it to improve aeration and water infiltration.” Thus, it can aid in encouraging somewhat deeper rooting of blueberries.

The Role of Calcium in Preventing Blossom End Rot

Blossom end rot (BER) is a physiological disorder caused by the lack of calcium in the developing fruit of tomato, pepper and watermelon. Calcium needs to be present in the soil by applying limestone but a supply of even soil moisture needs to be maintained throughout the planting as well. Calcium is taken up by plant roots through the water stream. Even if your soil contains plenty of calcium, if the soil is dry the plant roots cannot take it up.

The symptom of BER is a hard, leathery black rot on the bottom (blossom end) of the fruit. Early in the season, the first fruiting clusters on the plant can have BER because the root system of the young plant is not fully developed so it cannot pull up the calcium to supply both the leaves and fruit – so the calcium does not go into the fruit and a deficiency develops.

After the plants get larger, with more well-developed root systems, BER generally is not a problem, especially if the soil is wet down to a six-inch depth so the plants do not stress for moisture.

Do not try to apply calcium as a foliar spray, since calcium is not very well absorbed through leaves and fruit. The only efficient way for calcium to enter the plant is through the root system growing with ample soil moisture.

Brown Rot of Stone Fruits

Brown rot is a destructive disease of stone fruits (peach, nectarine, plum and cherry). The fungus overwinters on pits that have fallen on the ground and also on mummified fruits in the tree. Removing the pits or disking them into the soil will reduce the inoculum for infection.

During the winter, pits on the ground form cup-like structures around the edge of the pit. These are called ascus cups, and contain the fungal spores or “seeds” of the fungus. As temperatures increase, these ascus cups explode, releasing the spores to land on the newly developing fruits.

At first, the spores cannot penetrate the fruit to infect because the fruit has a low pH and a low sugar content. But after the fruits start to enlarge, especially before ripening has completed, the pH of the fruit increases as well as the sugar content.

At this stage, the spores can readily infect the fruit, turning them into brown mummies very quickly. Fungicide sprays are not effective at this point. Fungicide sprays that contain Captan or chlorothalonil need to be sprayed after petal fall, shuck split (when most shucks have split), first cover spray on fruit (seven days after shuck split) and then more cover sprays on fruit, spaced every 10 – 14 days apart, up until pre-harvest (three to four weeks before harvest). The shuck is the protective covering that covers the developing fruit before it falls off as the fruit enlarges.

Black Rot of Grape

In humid regions of the U.S., black rot is a destructive fungus disease that can shrivel a grape cluster into worthless mummies. These mummies can overwinter on the vineyard floor or in old hanging clusters on the vine. Spores of the fungus are produced within the diseased fruit during spring rains. Infected leaves develop reddish-brown, circular spots (lesions) on the upper leaf surface. As the lesions mature, the center becomes brown, and small, black, pimple-like fruiting bodies called pycnidia appear, usually arranged in a loose ring around the border of the lesion. The spores then blow to the young fruit, which become infected and turn dark brown, covered with numerous black pycnidia. Fruit infections occur from mid-bloom until the berries begin to color.

Apply Captan fungicide every 14 days after the new shoots are four inches long. During rainy periods, shorten the interval to seven to 10 days between sprays. Spray in the rain, if necessary, to maintain the schedule of applications. Always consult the label before making pesticide applications. Labels vary greatly among commercial products of the same material. It is important to refer to the label for the best timing and application rates.

Peach Tree Borer

Peach tree borers are caterpillars of a clear-winged moth. The moths resemble wasps, but the moths do not sting. They emerge throughout the growing season, but the vast majority of them are in flight between Aug. 15 and Sept. 15 in the Northeast. In the west, check with your Cooperative Extension Service to find out the best time to spray insecticides. There is only one generation per year.

In the Northeast, most of the borers can be managed preventively by treating with permethrin, cyfluthrin or other pyrethroid insecticide between Aug. 1 and 15 and making another application between Sept. 1 and 15. This coincides with peak moth flight. Make a single spray directed at the base of the trunk at the time of peak moth emergence – or, for small orchards, mix the insecticide in a bucket of water according to label directions and pour the mixture on the tree trunk, three feet above the ground, and let it soak into the ground at the base of the trunk to kill the young larvae. It is not necessary to treat higher into the tree since the moths lay eggs at the base of peaches, plums, cherry laurels and ornamental cherries. From these eggs hatch tiny, white caterpillars that bore into the bark and tunnel in the cambium at the base of the tree.

If you do not drench the lower tree trunk, the borers will go into the tree and kill it, due to the plugging of the tree’s vascular system. Many times, you will not notice that the tree is dying before it’s too late to do anything the following spring. The leaves can wilt and collapse suddenly, right after the fruit has set. Take notice and treat at the right time so you won’t become disappointed next year.

If many borers infest a tree, the cambium may be completely girdled beneath the bark and the tree will die. The borers pupate inside the infested tree during late spring and summer and then emerge as moths a few weeks later. Look for gummy plugs containing frass (insect excrement) or partially projecting pupal skins.

It is important to treat to prevent more borers from invading the tree. The only control otherwise is to try to gouge the borer out from under the bark with a flexible wire without injuring the tree excessively.