The best way to decide how much fertilizer to apply to strawberries grown on black plastic is to collect leaf and petiole samples and have them tested for nutrient content.

“Tissue sampling gives a ‘real time’ image of the nutrient status of the plant,” says Jeremy Pattison, Virginia Tech University Extension small fruits specialist. “It allows us to see potential deficiencies before the plants get distressed from them.”

The service is provided free by the state in North Carolina but not in Virginia, says Pattison. “I wish we had that service in Virginia. Our farmers can send samples to North Carolina, but it costs $20 per sample. That can get pretty expensive.”

There are several commercial services operating in Virginia that will send samples off for analysis for strawberry growers. “We like to see a grower taking maybe two samples at the beginning of the season, another when fruiting starts and one more in mid-fruiting for the second half of the season,” says Pattison.

In North Carolina, the Agronomic Division of the North Carolina Department of Agriculture and Consumer Services recommends collecting tissue samples at first bloom and continuing to do so every two weeks throughout flowering and fruiting.

The NCDA&CS laboratory measures actual concentrations of essential plant nutrients. Nutrients such as potassium, calcium, magnesium and boron affect fruit firmness, taste and appearance.

When levels of these nutrients are outside the ranges for optimal production, decreases in quality will eventually occur. Tissue analysis can identify nutrient shortages before symptoms appear, giving you time to adjust fertilization as needed.

John Strang and Joe Masabni, University of Kentucky Extension fruit specialists, say that knowing the nutritional status of your planting is a critical requirement for producing an excellent fruit crop.

“The only way the nutritional status can be assessed is through foliar analysis,” they say. “Soil tests provide only a portion of the picture and tell only what is in the soil. Tissue analysis shows which nutrients the plant is actually absorbing.”

This facilitates fine-tuning of the fertilization program. “It lets the grower know when an element is becoming deficient before symptoms show up and allows for correction of the problem before fruit quality and yield suffer,” says Strang.

Unlike Southeastern growers, most Kentucky growers plant on matted rows rather than on plastic. “One tissue analysis a year is plenty for matted row production,” says Strang.

By comparison, weather and pests may be somewhat unpredictable, and remedial options are not always available for the damage they cause, says North Carolina Department of Agriculture Regional Agronomist Rick Morris. “But there is no reason for yield to be compromised by a nutritional problem.”

At least half of Virginia’s commercial farmers are tissue sampling now, says Pattison. “We certainly recommend it. I can help a farmer a lot better if he is tissue sampling. The value of tissue sampling on a strawberry farm is consistently high from year to year.”

Here’s how to collect a tissue samples from strawberry plants and submit them for analysis, according to the North Carolina Department of Agriculture:

• Select the most recently mature, trifoliate leaves. These leaves will be full-sized and green and consist of one petiole or leaf stalk with three leaflets and are usually located three to five leaves back from the growing point.

• Avoid collecting damaged tissue.

• Detach the petioles from the leaves as you collect them, but submit them together as one sample.

• Include leaves and petioles from 20 to 25 locations within a uniform area in each sample. The sample should be representative; that is, all of the plant material in a single sample should be from the same variety, growing on the same soil type, planted at the same time and having the same management history.

• When submitting tissue samples, be sure to fill out the information sheet completely, including fertilization history and environmental conditions. It is particularly important to provide the name of the strawberry variety being grown as well as its stage of growth at the time of sampling. Stage of growth refers to week of bloom and can be coded B1 through B12 (first through 12th week of bloom). Accurate management recommendations depend on this information.

Proper interpretation of the tissue analysis requires that a soil sample be taken at the same time or there should be a recent analysis from the block where the tissue sample was taken, says Strang. The laboratory will send the results of the tissue analysis directly to the grower with recommendations.

“It is not necessary to sample a block every season, because nutrient levels do not change that rapidly. It is generally recommended that a block be sampled once every three years.”

Dust or pesticides on the leaves will affect the analysis, particularly for zinc, manganese and iron, says Strang.

“Select clean leaves, or the leaves may be washed,” he says. “Dirty leaves should be washed very quickly in water with a small amount of liquid dishwashing soap and then rapidly rinsed through three containers of water. Leaves should then be air dried on a paper towel and sent to the tissue analysis lab.”

In North Carolina, strawberry tissue analysis costs $7 per sample and requires both leaves and petioles. Analysis of leaf blades reveals nutrient deficiencies or excesses, while analysis of petioles gives a good indication of the amount of nitrate nitrogen currently available for crop growth and development.

When test results show nutrient levels to be out of the optimal ranges, the plant analysis report provides recommendations for corrective action.

A guide to collecting and submitting strawberry tissue samples in North Carolina is available online at http://www.ncagr.com/agronomi/pictorial.htm. NCDA & CS regional agronomists are also available throughout the state to offer guidance and answer questions about sampling and fertilization.