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February 2013 Archives

February 1, 2013 Issue

Tomato Blossom End Rot - Facts & Control

Karl Foord - Extension Educator, Horticulture

In anticipation of spring tomatoes, please consider your tomato systems and avoid one of the scourges of gardening - tomato blossom end rot.

Michelle Grabowski

Photo 1: Blossom End Rot

Michelle Grabowski

Photo 2: Blossom End Rot

Symptoms of blossom end rot

Water soaked areas at the blossom end of the fruit usually appear when the fruits are one third to one half full size (Photo 1). This enlarges and darkens as the fruit matures (Photos 2 & 3).

Michelle Grabowski

Photo 3: Blossom End Rot

These large sunken lesions dry out flatten and become black and leathery. Typically the first fruit are most severely affected, and later developing fruit can be unaffected.

Causes and the role of calcium

Blossom end rot is a "physiological disorder" induced by a localized calcium deficiency in the fruit. The incidence of the disorder is usually not due to a lack of calcium in the soil, but rather due to factors affecting the uptake and translocation of calcium.
On a cellular level calcium is a critical component of cell walls (a structural nutrient). So when calcium is limiting cell walls cannot form properly and rapidly growing parts of the plant suffer breakdown. As a structural component calcium once incorporated into a cell wall is not mobile within the plant.

At the plant level, the end of the fruit is an area of rapid growth and has a high need for calcium as do other rapid growth areas like meristems. If 90% of the calcium that a mature fruit contains is already in the fruit by the time it is ½ - ¾" in diameter then the critical time for calcium uptake is early in the development of the fruit.

Soil calcium and plant uptake

Calcium uptake is associated with water uptake. Thus anything that interferes with water uptake can create calcium deficiencies. Dry or wet soils interfere with water uptake in different ways but both can lead to calcium problems. The strongest sink for calcium is actively transpiring leaves because they are actively pulling water. Other plant structures are not transpiring near the degree that leaves are and thus function as poorer calcium sinks. A waxy cuticle develops on the fruit when it is ½ - ¾ "in diameter which reduces transpiration and thus weakens the fruit as a calcium sink.

The fruit is competing with leaf tissue for calcium so a higher fruit to leaf ratio reduces the relative strength of the leaf as a calcium sink allowing more calcium to be allocated to growing fruits. This adds to the logic recommending pruning of tomato sucker shoots.

Control of Blossom End Rot

Maintain even and adequate soil moisture; mulch aids in this process. Avoid poorly drained and cool soils. Avoid over- fertilizing with nitrogen which creates excessive vegetation. Avoid ammonium based fertilizers as ammonia inhibits uptake of calcium. Use nitrate as the main source of N in fertilizers. Choose cultivars that have fewer tendencies to demonstrate blossom end rot. Use soil test data to maintain proper nutrition and optimum pH in the 6 - 6.5 range.

Foliar applications of calcium

There seems to be disagreement about the effectiveness of foliar applications of calcium. The logic on the ineffective side is that calcium is immobile in the plant and will not translocate to the fruit from material sprayed on the leaves. The response is to spray on the fruit. However, a waxy cuticle develops on the fruit when it is ½ - ¾ "in diameter which reduces transpiration and perhaps direct absorption of sprayed calcium.

Often blossom end rot decreases as the season progresses. This could be due to weather effects, warmer soils, or a slowing of vegetative growth all of which would make it appear that early applications of calcium have been effective.

Perhaps foliar sprays applied on plants prior to the first cluster of fruit or directly on small fruit can be used to supplement calcium. Calcium nitrate and chelated calcium are the safest sources of calcium to be applied as a spray. However spray applications of calcium are no substitute for proper nutrition and water management.

If calcium is best allocated by the plants xylem water conduction system, then keeping this system functioning optimally is the best course of action.

Editors note: This article was developed from a presentation created by Dr. Carl Rosen and Michelle Grabowski and delivered by Dr. Carl Rosen at the Upper Midwest Regional Fruit and Vegetable Growers Conference.

Pavement Ants in Homes During Winter

Jeffrey Hahn, Asst. Extension Entomologist

Winter is not a time when you typically expect to encounter ants in your home. However, it happens more often than you might think. One of the more common ants found in homes and other buildings is pavement ants. This ant is 1/8th inch long and is reddish brown, although it can range in color from light brown to dark brown to almost black. With magnification you can see that this ant has a two-segmented petiole (the waist between the thorax and the abdomen) and two short spines projecting from the thorax.

Jeff Hahn

Photo 1: Pavement ant worker. Note the two-segmented petiole and two small spines on the abdomen.

Pavement ants like to nest in the soil under or besides objects, such as stones, bricks, sidewalks, and driveways. They can also nest under the concrete slabs of homes as well as in wall voids. They typically nest near a heating source which allows the ants to be active during winter. They can follow pipes that go through slab to move up into the living quarters of homes thorough expansion joints, under baseboards and floor registers. Sometimes large numbers of winged pavement ants are found which are the reproductives of the colony, i.e. females and males.

Pavement ants can infest foods; they like protein and grease, such as meats, cheese, dead insects, dry pet food, and peanut butter, as well as a variety of sweets. Other than that, pavement ants are mostly annoying and are not particularly damaging to homes.

If you are finding pavement ants in your home, try to determine from where they entering. If you can determine they are moving through a crack, e.g. in an expansion joint, try to seal it to help keep pavement ants out. If you are not able to find how they are getting into your home, then try baiting them.

Jeff Hahn

Photo 2: Pavement ant swarmers can be sometimes seen indoors. They are just a nuisance.

Select a bait that is effective for grease feeding ants and place it where you are commonly finding them. Don't be surprised if there is an increase in the number of workers that are around the bait. That's good, the more ants that take bait back to the nest, the more likely you can eliminate it. Don't spray the foraging workers. It doesn't have any impact on the colony and will also lessen the ability of the workers to take bait back to the nest.

If you are not successful in your efforts to get rid of pavement ants or you would rather have someone control them for you from the start, talk to a professional pest management service about treating your ants.

Not all ants found indoors during winter will be pavement ants. People can also potentially see carpenter ants, Pharaoh ants, yellow ants, and thief ants in their homes during the winter. Their habits differ as do the methods for treating them. If you have any doubt as to what kind of ant problem you have, get them identified them by an expert.

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