Posts Tagged ‘fruit’

Its All About Light

Thursday, April 29th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Production of high yields of quality fruit requires adapted varieties, close attention to disease and insect management, balanced plant nutrients, and good weather conditions. One of the other key areas that growers need to consider is light. Leaves require adequate light levels to produce sugars by photosynthesis. These sugars are then translocated into developing fruit. Sugars also provide the building blocks of other flavor components. With this in mind, a very important aspect of fruit management is to insure even light distribution throughout the plant canopy. This applies equally to small fruits and tree fruits.

The following are some considerations to achieve this even light distribution and to manage for the best combination of yield and fruit quality.

1) Play close attention to plant densities and do not overcrowd plants. While more plants often means higher yields, excess shading at high populations can lead to reduced quality. Crops like matted row strawberries bear the most fruit and best quality fruit on the edges of the row. In most fruit crops, fruits on the interior of dense canopies often have poorer color, reduced sugars, and poorer flavor.

2) Choose pruning and training systems that allow for even light distribution. In fruits such as peaches, this is achieved by pruning so that scaffold branches are arranged in a open form V or vase shaped form. In crops that use a central leader system such as apples, it means pruning to appropriate spacings and orientations between scaffolds to allow for good light penetration. In summer bearing brambles, this means having trellis wires arranged so that fruiting canes are to the outside where they can receive the most light and training new canes to the in the middle. Pruning canes higher will also allow for more light along the length of the cane, however, they should not be so tall that they shade neighboring rows.

3) Thinning fruiting material and thinning foliage is often necessary for good fruit quality, color development, and uniform ripening. Leaf thinning is practiced in grapes for this reason. Thinning of blueberry canes to remove old and weak material is another example as is detail pruning of many tree fruits to remove excess fruiting wood and allow in more light.

Pear and Apple Fire Blight: Maryblyt Predictions Can Aid in Disease Management

Thursday, April 8th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Adapted from an article in Ky Pest News April 6, 2010 #1224 by John Hartman, Extension Plant Pathologist, University of Kentucky.

Flowering pears (Pyrus calleryana), grown in many landscapes, are in full bloom in most of Delaware. Pears grown for fruit in backyards and orchards in the region are also in flower now. Fire blight can be a devastating disease of nursery and landscape flowering pears and can also damage pears (both Asian and European) in fruit orchards.

Fire blight primary infections occur during bloom. During warm spring weather, the causal bacteria (Erwinia amylovora) grow on the surface of flower parts such as the stigma. After several warm days, high populations of bacteria become available to be washed by rainfall or even heavy dew into the nectaries at the base of the flowers. Once inside the flower, the bacteria continue to grow, killing the fruit spur and spreading into the subtending twigs and branches. Disease build-up from these infections leads to shoot infections, the most noticeable part of this disease, which appears later.

This year, a new version of a computer program called Maryblyt has become available to help nursery growers and orchardists make decisions to manage fire blight disease. This new version of the program, called Maryblyt 7, utilizes Windows-based computers and was updated by plant pathologists Dr. A. R. Biggs (Tree Fruit Research and Education Center, Kearneysville West Virginia) and Dr. W. W. Turechek, (USDA-ARS, Florida). They have indicated that it is free for the downloading by growers, extension agents and crop advisors.

Go to the following link to download a copy of the new Maryblyt 7 program.

This is a good time for growers to get the program running for the 2010 season. Growers can enter the data themselves and the program automatically provides a chart and graph of fire blight status. Growers only need to provide date, growth stage, daily maximum and minimum temperatures, and rainfall (or heavy dew) for their nursery or orchard. Weather data are entered into the program starting at green tip (perhaps sometime between March 21-24 this year) so weather data from recent weeks will need to be found. Growers wanting weather data specific to their orchard or nursery can purchase a maximum/minimum thermometer and a rain gauge at the hardware store. By knowing when infection is expected, preventive orchard and nursery applications of streptomycin can be used in a timely way.

Success with Blueberries

Thursday, April 8th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

There has been an increase in interest with blueberry production in Delaware over the past 5 years. Blueberries can be a very profitable crop, especially for growers that direct market. As a perennial shrub-like crop, blueberries will take 5 or more years to come into full production but can be productive for decades. It is critical therefore to make sure that plants get off to the right start. Blueberries have exacting soil modification requirements that must be addressed. They are native to areas with acid soils that have high organic matter in the surface but with sand below and with water relatively close to the surface. However, they do not tolerate waterlogged soils.

There are 5 key factors critical to establishing blueberries.

1) Acidify the soil. Blueberries require acid soils with a pH in the 4.5-5.2 range (target 4.8). Most of our cultivated soils have pHs much higher than this. Therefore soils must be acidified. The material commonly used to acidify soils is elemental sulfur. However, sulfur must be converted by microorganisms to release the acidity so it acidifies only when soils are warm. Plan one year ahead of time to acidify the soils. On a sandy loam soil, about 1000 lbs of sulfur per acre are required to lower the pH to the desired level. You should not plant until the soil has been acidified.

2) Provide good drainage. Make sure that water drains away from the planting site and does not collect. It may be necessary to make low, wide ridges to improve drainage and move excess water away from plants. Avoid planting in sites that are poorly drained or that have high water tables in the winter.

3) Increase organic matter in the area that is to be planted prior to planting. This is commonly done through the addition of materials such as peat moss mixed directly into the planting hole (mix at one gallon of peat with backfill soil for each plant during planting). You may also use other materials such as composted saw dust, bark fines, or other partially rotted materials as long as they are acid (have low pHs). You can use up to half by volume of these materials mixed with soil in the hole. Do not use manures, high pH composts, or spent mushroom soil. You may also choose to modify the entire planting strip before planting. Apply 2-4 inches of these organic materials (such as composted sawdust or bark fines) and work them into the soil in a 3-6 foot strip where the blueberries are to be planted.

4) Mulch immediately after planting with a 4 inch layer of organic material. Common materials are aged sawdust or bark mulch. This mulch is critical to protect the shallow roots and provides additional organic matter as it decomposes (reapply as necessary).

5) Install drip irrigation and provide irrigation water through the drip as needed. Blueberries do best in moist (not wet) soil conditions. Drip tubing should be thick walled for long term use and should be placed under the mulch.

Peach Pruning Best in March-April

Thursday, March 4th, 2010

Gordon Johnson, Extension Fruit & Vegetable Specialist;

Research has shown that peach tree pruning is best done in March or April.

In past years with mild winters, there has been a tendency to prune on the early side. With the snow and cold weather in 2010 this has not been as much of an issue this year.

Pruning is done to remove suckers, manage fruit loads, manage vigor, manage tree shape, increase light penetration, and remove damaged or weak wood.

Pruning earlier than March increases the risk of cold injury to buds because trees are stimulated metabolically by the pruning. It is advised to only do pruning to remove dead or damaged wood during the winter.

As trees start to become active in March, there is little or no increase in cold injury to buds by pruning. Sucker removal and removal of weak fruiting branches can be done at this time, along with managing the shape and openness of the tree. While selective removal of excess fruiting material can be done, the full fruiting potential cannot be evaluated until plants start to bloom. In addition, winter injury or poor plant vigor cannot be determined accurately in March. This may lead to excessive pruning of weaker trees that could be detrimental.

You can also prune peaches when plants start to bloom through the month of April. This allows for better assessment of fruiting potential and selective thinning of fruiting wood to manage crop loads. It also stimulates plants to produce more growth. In peach orchards where reduced plant vigor or damage is suspected, delaying pruning to late April or early May will allow for accurate assessment of tree status so that pruning can be matched to the level of vigor or extent of damage.

Summer pruning (July) can be beneficial, especially in trees with excessive growth. However, because peaches fruit the following year on wood produced this year, any removal of this year’s growth will reduce fruiting wood for next year. Therefore, take care not to do excessive summer pruning. August pruning is not recommended on trees still in fruit but can be done on earlier cropped trees or non-bearing trees.

Avoid peach pruning from September through February and mid-May through June.

For a good article on the subject by Jerome Frecon, Agricultural Agent at Rutgers University, go to

Cold Temperature Damage in Fruit Crops

Friday, May 1st, 2009

Gordon Johnson, Extension Ag Agent, Kent Co.;

We have seen considerable cold temperature damage to fruit crops in parts of Delaware and the Eastern Shore of Maryland. In particular, certain mid-season peach varieties have severely reduced crops; some varieties will not have enough fruit to warrant harvest, and other varieties will have a reduced crop. Early peaches and those up to the Red Haven season have better sets and will need to be thinned. Later peaches also have better sets.

Matted row strawberries that were uncovered have suffered anywhere from a 15% to over 50 % loss of flowers due freeze damage in some areas. Brambles (raspberries and blackberries), have also had significant winter damage to canes resulting in the need for additional pruning back of dead material.

These losses can be attributed to three cold weather events. On March 3 and 4, low temperatures were near 0°F in some areas. The second damaging event was on March 25 where temperatures dropped to 22°F and the third event was on April 13 where low temperatures reached 26°F in some areas.