| [Image: Louisiana Strawberry Crop ] |
| [Image: Planting Depth of Strawberries ] |
| [Image: Row Covers for Strawberries ] |
Strawberries can be grown in all parts of the state and have been an important horticulture crop for many years. Tangipahoa and Livingston parishes have been the traditional commercial production areas. It requires a high input of capital as well as effort to establish a strawberry planting. However, with a good crop, good harvest labor and excess to markets, strawberries can return high profits.
Varieties
Strawberry varieties recommend for commercial production in Louisiana are:
Strawberry Festival -- developed by the University of Florida. Early-maturing fruit, good taste, some resistance to Anthracnose fruit rot. It is the most popular variety in the Louisiana strawberry industry.
Camarosa -- developed by the University of California. Early-maturing, average size, good firmness, high yields. The maturity of the fruit tends to be spread out throughout the season.
Camino Real -- developed by the University of California. Later than Camarosa, produces large to extra-large berries, firm, good shaped fruit with good quality.
Source of Plants:
Within the last 20 years, the production of strawberry plants in Louisiana has become difficult because of the incidence of the disease crown rot. Few plants are produced in the state. Growers obtain bare root plants from commercial nurseries in California, Michigan, Oregon, Quebec, Canada, and Nova Scotia. Plants from each source have unique characteristics and problems. Those interested in producing strawberries should check with a county agent for a list of individuals handling plants.
Canada (Quebec and Ontario) Plants: Large, leafy plants with a good root system and early-season maturity. The most popular source of plants for the Louisiana strawberry industry at this time.
California Plants: Plants without leaves. The maturity of the fruit depends on location of the nursery. Plants from nurseries located at high elevations are generally early while plants from lower elevations are medium in maturity. These plants need to be planted in early October.
Canadian (Nova Scotia) Plants: Large, leafy plants with a medium-early season maturity. The maturity of the fruit tends to concentrate at mid season, resulting in a large volume of fruit to harvest and market within 10 -14 days.
Plug Plants
In the last several years, plug plants from Quebec have become popular. These plants are rooted in a small peat pot or peat pellets. The plug plants have an established root system. They have the advantage of easier transplanting, complete survival and heavy early production.
Site Selection
Deep, sandy soils with good surface and subsurface drainage are excellent soils for strawberries. A soil that can hold up spray equipment when the soil is wet is a big advantage in controlling diseases during times of wet weather. Plantings should be made in an area where a good water supply is available for irrigation and frost control.
Soil Preparation
Soil preparation should begin in August (six to eight weeks before planting in mid-October -- early November). Summer cover crops such as cow peas, soybeans or Sudan grass are very desirable for the production of strawberries. The cover crop should be turned under in early August to allow crop residue to decompose and mix with the soil before planting in October. The most desirable row width is 42 inches to 48 inches. Rows should be 8 inches to 10 inches high after they have settled from rain. Rows should be pulled up well ahead of time and allowed to firm up before laying plastic. A firm row will help ensure a good tight fit of the plastic on the row.
Recommended Soil pH & Fertilization
Strawberries prefer to be grown on the acid side. A pH 5.2-6.0, with calcium levels of 700 -1200 ppm and 100-150 ppm magnesium. It is important to pay attention to the calcium levels in the soil. Low soil calcium levels can enhance the occurrence of anthracnose fruit rot on berries.
Apply 50 - 80 lbs./A of nitrogen and 60 - 150 lbs./A of phosphorus and potassium preplant. To avoid fertilizer burn, growers should wait for a rain (1-2 inches) after applying fertilizer before they put out plastic and plant berries.
Example : 600 to 800 lbs. of 8-24-24 per acre, or 800 to 1000 lbs. of 5-10-5 or 13-13-13 per acre preplant.
Plastic Mulch and Fumigation
Strawberries should be mulched with black plastic mulch to prevent splashing of soil particles on the fruit from irrigation and rain. It is extremely important that the plastic mulch be snug to the surface of the row and covered well on both sides of the row with soil. The correct use of drip irrigation will help to produce high yields of good quality strawberries. Soil sterilization with methyl bromide is effective for the control of soil fungi and bacteria, soil insects, nematodes and weeds. Methyl bromide is a liquid under pressure that becomes a gas when applied to the soil. Methyl bromide is mixed with chloropicrin (tear gas) for a warming agent. The chloropicrin also is effective on the disease organisms in the soil.
Apply 150 to 200 pounds of methyl bromide per acre 6 to 8 inches deep on firmly shaped beds during the same operation in which the plastic is laid. For best results, leave the soil sterilant under the plastic for at least 48 hours. Remove the gas from under the plastic by making slits in the plastic with a simple mechanical cutter where the plants are to be transplanted 10 to 14 days before transplanting. A cylinder of methyl bromide and 4 to 5 rows of plastic are required for an acre of ground.
Drip Irrigation
The correct use of drip irrigation provides an ideal soil moisture level for plant growth. The irrigation time interval depends upon the rate of water evaporation, temperature, the stage of plant development and the flow rate of the drip tube. The irrigation interval starts out short and increases as the plant develops and the temperature increases. The demand for water is greatest during the fruit-setting and fruit-sizing stage. It is important for the soil to be at the ideal soil moisture level during these times to obtain high yields of high-quality fruit.
Growers who are using drip irrigation for the first time are encouraged to water by a set schedule. Within time, the growers will be able to fine tune the irrigation schedule to their own fields.
It is very important for growers to check their fields every 2 or 3 days to determine if the time intervals for irrigation need to be increased or decreased. The soil in the root zone (6- 8 inches deep) should be moist and form a loose ball when squeezed in your hand. The soil should never be saturated. Water should not run from under the plastic into the middle of the row.
Drip Irrigation Schedule for Strawberries
|
Crop Stage |
Weeks |
South La. |
North La. |
|
|
|
Minutes/Day1 |
Minutes/Day |
|
Young Plants |
4-6 |
30 |
30 |
|
Growing Plants |
8-10 |
20 |
20 |
|
Early Harvest |
6 |
25 |
25 |
|
Main Harvest |
12-16 |
|
|
|
February |
|
30 |
30 |
|
March |
|
30 |
40 |
|
April |
|
50 |
45 |
|
May |
|
50 |
60 |
|
June |
|
|
70 |
1All time intervals for irrigation are based on the use of a drip tube with a flow rate of 1/2 gallon per minute per 100 foot.
Fertigation
Sidedressing can be done by injecting the fertilizer through the drip lines by using an injection device. This method is known as fertigation. Growers apply some of the nitrogen fertilizer preplant (40-80 lbs. of N/A) and inject the sidedressing nitrogen in equal increments from bloom and fruit set and continue to harvest. The nitrogen fertilizer is injected into the system at a rate of 3/4 pound of N/A per day or 5 1/4 pounds of N/A per week.
Example: 600-700 lbs of 8-24-24/A preplant. Start fertigation 3 to 4 weeks after transplanting and continue through harvest. Inject 32 lbs of CaNO3 or 30 lbs of KNO3 per acre per week. The greenhouse grade of CaNO3 or KNO3 is easier to dissolve and inject.
Foliar Samples
Growers are encouraged to take foliar samples (most recent full-sized leaf) monthly to monitor the levels of nutrients in the plants. The results of the foliar samples can be used to adjust the fertility program in the field. Contact your county agent for instruction on taking foliar samples.
Planting Arrangement
Double-set rows usually yield more berries per acre, but single-set plants yield more fruit per plant. A field of double-set rows will generally produce more berries in the early season than a single-set row field. On double-planted rows, the incidence of disease and insect may increase since the dense foliage is harder to penetrate with fungicides and insecticides.
Plants/Acre
The exact number of plants per acre will vary with the planting arrangement, row size and the spacing between plants.
- 8,000 to 10,000 plants/A for single set row.
- 15,000 to 18,000 plants/A - double set rows
Spacing
- Single-set row - 14, 16 or 18 inches
- Double-set row - 16 or 18 inches apart alternately along the row with a 12- to 14-inch spacing between the rows of plants.
Transplanting
Early October through early November. Best yields are obtained when transplanting is done by mid- to late October.
Only well-developed plants with good root systems should be transplanted. Best yields are usually realized when transplanting is done in mid-October to early November. A wheel with bolts or blades attached is used to mark where the plants will be planted. Use a trowel to make slits to plant the plants. A 3-inch to 6-inch slit is large enough for the strawberry plant on plastic mulch. The bud and crown of the plant should be above ground and the roots below ground level. Plants set too high will suffer from root injury from exposure. Those set too low will usually suffer from bud or crown injury. Plants set with their roots bent will lack vigor and have poor yields. Firm the soil around the roots to prevent drying out. After the plot has been planted, water the plants to settle the soil around the roots. Strawberries require a lot of water after transplanting. It is not uncommon for growers to water 4 to 5 hours in the middle of the day for 5 to 10 days after planting.
Fungicide Dips before Planting
Bare-root strawberry plants may be dipped in a fungicide suspension prior to planting to provide early-season control of root and crown rot diseases. Prior to dipping, the plants should be washed free of any adhering soil. The entire plant should then be dipped in the fungicide solution for 2-5 minutes or 15-30 minutes depending upon the fungicide used. Plants should then be set in the field as soon as possible. Consult the Louisiana Plant Disease Control Guide for a list of fungicides that can be used for disease control in Louisiana strawberries.
Pollination Requirements
Strawberries are pollinated by wind and bees. Low temperatures and extended periods of rain interfere with the pollination process, resulting in deformed, crippled or cracked fruit. Bees (one or two hives/acre) seem to help overcome some of the problems associated with pollination.
Recommended Herbicides
Plastic mulch and fumigation with methyl bromide control most of the weeds on top of the row. Weeds are still a problem between the rows. Failure to control weeds in row middles will enhance the development of mites.
Premergence Herbicides -- After Laying Plastic Mulch
Goal can be applied soon after the plastic mulch is put down. A 30-day interval from application to planting is required. This is a very effective treatment in controlling weeds in row middles before planting. This treatment also keeps the field clean until the next herbicide application.
Premergence Herbicides -- After Planting
Devrinol can be applied after transplanting. It is best to water-in Devrinol to a depth of 2 to 4 inches after application.
Most growers apply Simazine/Princep to row middles after the plants have become established (mid-November to early December). This is an effective means of controlling winter weeds in the row middles.
Post-emergence Herbicides -- After planting
Gramoxone and Aim are cleared for use as a post-emergence directed spray to row middles with shields.
Select is cleared for post-emergence grass control on strawberries.
Frost Protection
Sprinkler systems are used for frost control in strawberries. Ice forming on the plants acts as insulation to prevent damage. As long as the supply of water is continuous, there will be a slight amount of heat given off as the water turns to ice. This heat will serve to maintain the temperature around the plant at 32 degrees. Frost control should be turned on when the temperature in the field drops to 34 -33 degrees and is expected to go lower. Water should be left on until the ice that has formed on the plants thaws.
Row Covers
Row covers made of light polypropylene fabric can be placed directly on top of the crop to protect strawberries from frost. The heavier they are, the more protection these covers provide. Covers of 1 ounce per square foot are the most popular. These covers in combination with sprinkler irrigation have provided protection from frost. These covers also trap heat during the daytime hours, pushing plant development and earlier harvest. Most growers get covers wide enough to fit in between the sprinkler lines. Plastic 10-pound rice bags filled with sand and spaced every 10 to 20 feet are used to hold the covers down (100 bags per acre).
The covers should be put on when the grower decides to start saving blooms. The covers should be removed during the day to allow pollination and spraying. It requires 4 to 6 people 15 to 20 minutes to uncover or re-cover an acre. The berries should be re-covered at night. It is best to cover the berries well before a hard freeze. It is difficult to handle row covers when they are wet and in high wind conditions.
Growers need to restrict the area covered to the amount of available labor they have to handle the covers. It requires 4 men, 15 to 30 minutes to remove or re-cover an acre of strawberries with row covers. The use of row covers creates an area of higher temperatures and high humidity around the plants. This tends to enhance the development of gray mold on the fruit and mites in the field. Growers need to monitor the disease and mite situation closely and use the correct control measure to be successful with row covers.
The use of wire hoops to hold the row covers off the berries has become popular in the last several years. A square-shaped hoop (18 inches tall and 20-24 inches wide) is made of heavy-gauge wire. A small circle about the size of quarter is made in each corner of the hoop to provide tension. A hoop is placed every ten feet. Tomato tying twine is run on each side of the hoop to provide support for the row cover. The twine is wrapped around the circle in each corner of the hoop. The twine is pulled tight and tied to a rebar rod (18 inches long ) to anchor the hoops at the end of each row. The covers are pulled over the hoops and held down with sand bags. It takes 1,000-1,100 hoops per acre ($1.10+/hoop) and 40-45 man hours to install hoop and end bars and 10 man hours to run the strings. The cost is estimated at $1,600-$1,700 per acre.
It is difficult to get two years out of a row cover because of tears caused by moving and the difficulty in picking them up and storing them after the season. Row covers are expensive; the cost of covering an acre ranges between $1,000 to $1,700, depending on the thickness. They should be used only when growers make a serious commitment to the production of strawberries. All other cultural practices must be used successfully to obtain the full benefits of row covers.
Harvest Information
Harvest berries early in the morning when the weather is cool. Berries should be handled carefully to avoid bruising. They should be pinched from the plant rather than pulled. Pinching leaves the caps (calyx) on the fruit and also provides a 1\2-inch stem attached to the fruit to handle the fruit without touching. A harvest every third day is usually required for maximum yields of high-quality fruit.
Fruit for local, same-day sales is picked fully ripe, totally red. Fruit for shipping is picked with about 3/4 of the surface area pink or red.
Strawberries are harvested, graded and packed by the pickers in the field. They are packed into fiberboard flats containing 12 one-pint baskets. Plastic clam shell quart containers with an attached cover are becoming more popular. The shelf life of the berries is extended with the clam shells. Pickers should always use a picking cart to keep flats off the ground.
The packing of strawberries by the pickers in the field decreases the handling steps and reduces the possibility of damage. This system places a good deal of responsibility of maintaining fruit quality on the pickers. If the fruit is not picked and packed carefully, all other attempts to maintain fruit quality are useless.
Pack only firm, well-shaped berries of good size and desired ripeness for the market. If overripe berries are packed, they can cause firm ones to decay before reaching their destination. Soft, bruised and overripe fruits should be discarded. Discard any berries with decay. Rotten, deformed or damaged berries should be removed from the plant at each harvest. Remove the discarded berries from the field to prevent the spread of disease.
Fruit should be handled gently at all times. Anytime a fruit is bruised, that area will discolor. In addition, bruising increases water loss. Trying to hold too many fruit at one time will result in bruising. Harvested strawberries should be placed, not dropped, in the flats. Overfilling flats causes bruising.
The flats should be stacked directly onto pallets for shipping. This eliminates the need for further handling of individual flats. Travel over rough field roads can damage packed strawberries. Harvested berries should be kept in the shade and moved to a cooler within 1/2 to 1 hour after picking. Protect berries from heat and dust as much as possible when hauling.
Harvest Labor
Generally, berries are harvested on a task system. Good pickers can average 3-4 flats per hour (harvested and packed) in good, high-yielding strawberries. The importance of picker training and supervision cannot be overemphasized. The quality of the pack depends on the picker. A financial incentive should be offered to pickers who pack a good grade of strawberries and remain with the grower throughout the season.
Harvest efficiency can be increased by avoiding rows longer than 200 to 300 feet. The shorter rows minimize the time pickers spend traveling between the flat collection point and the field. Collection points on both ends of a field can save considerable time.
All diseased or deformed fruit should never be put in the flat. Discarded fruit should never be thrown in the middles. This fruit needs to be remove from the field to prevent the build-up of diseases.
Good yields: Drip irrigation, row cover, strawberry Festivals 2,000-2,500 flats/A, Camarosa 2,500-2,800 flats/acre
Post Harvest Handling
Berries should be cooled to 32 degrees as soon after harvest as possible. Forced-air cooling is the preferred method for removing field heat from strawberries. Strawberries should be stored at 32 to 34 degrees. Strawberries are a very perishable crop. Holding periods should be kept as short as possible.
Grades of strawberries are U.S. 1, Combination and U.S. 2. The principal grade on the market is U.S. 1. U.S. 1 strawberries are of one variety with the cap attached and are firm, not overripe or underdeveloped, and free from mold or decay and damage caused by dirt, moisture, foreign matter, disease, insects, mechanical or other means. Each fruit has at least 3/4 of its surface showing a pink or red color. The minimum diameter of each strawberry is not less that 3/4 inch.
Deformed Fruit
Many of the early berries are deformed. This is due to low temperatures and cloudy and rainy weather, which interfere with the pollination process. The pollination and the development of seeds enhance the development of the fleshy part of the berry. The number of deformed fruit will decrease as the weather conditions improve. The deformed or crippled berries should never be put into the finish packed flats. All discarded fruit needs to be removed from the field.
Disease Control
Several diseases attack strawberries each year. Early in the season, foliar diseases are more important. Leaf spot (also called bird eye spot and rust) is very common. It produces small spots with white centers and purple margins. These can coalesce and defoliate the plants. Angular leaf spot is most common during the winter after periods of rain or when growers are using frost-control sprinklers. This bacterial disease produces small irregular spots that are most noticeable on the bottom of the leaf. The spots often look water-soaked and shiny.
Two fruit rots commonly occur on strawberries. They are gray mold and fruit anthracnose. As the name implies, gray mold produces sunken brown-to-salmon lesions with a white to gray fungal growth on the fruit. Gray mold usually develops at the calyx end of the fruit first. Anthracnose may appear anywhere on the fruit and may rot the tip end of small green berries. Diseases are controlled by using recommended fungicides. It is extremely important to select the proper fungicides, because many of them are very specific and will not control all diseases.
Consult the Louisiana Plant Disease Control Guide for a list of fungicides that can be used for disease control in Louisiana strawberries.
Insect Control
Many types of insects, mites, and snails attack strawberries. These include aphids, strawberry weevils, strawberry leaf rollers, armyworms, flea beetles, lygus bugs, leafhoppers, tarnished plant bugs, snails and slugs, two-spotted mites, spittle bugs, crickets and mole crickets and fire ants. A variety of insecticides are registered for control of these insect and other invertebrate pests of strawberries. Consult the Louisiana Insect Pest Management Guide for a spray schedule.
The two-spotted spider mite is the most persistent and damaging pest of strawberry production in Louisiana. It has a strong preference for hot and dry conditions. Mites damage plants when they pierce and feed on leaf cells, resulting in the death of the cell. The damage causes a stippling effect, which appears bronze. If left uncontrolled, mite populations rapidly exceed threshold levels and cause visible damage, bronzing on upper leaf surfaces, purplish and distorted leaves, brown to dry foliage, reduced flowering and stunted plants. Many mite infestations begin in new strawberry plantings along field margins close to or adjacent to areas with mite infestations such as maturing vegetable crops or weedy areas.
Two-spotted spider mite adults may reach 1/60 inch in length. With a naked eye, mites appear as dark-green dots moving on the underside of strawberry leaves. With the help of a 10x magnifying lens or an optivisor, adult mites may be seen as yellowish or pale green with a large dark blotch on each side of the body and eight legs. The mobile, immature stages are referred to as nymphs and are pale yellow, greenish or straw colored. Depending on the stage of development, nymphs may have six or eight legs. Minute and spherical eggs, which are pale yellow to green in color, are deposited on the underside of leaves among webbing produced by male adults. The lifecycle from egg to adult is usually two to three weeks in Louisiana.
It is important to begin monitoring strawberry fields in Louisiana once every two weeks starting in mid-October, and continue sampling once every week from January until three weeks before the end of the harvest season. Scout for spider mites by using a 10x hand lens. Make sure to inspect not only for two-spotted spider mites nymph and adults but also for predatory mites to see if natural enemies are controlling two-spotted spider mites. A good monitoring plan includes sampling field edges, middles and field corners. Inspect the underside of leaflets. Choose fully developed leaflets from the middle tier. Avoid leaves that are too young or too old. Select one leaflet per plant and inspect 10 to 20 plants, depending on the size of the field. Treatments are justified when an average of five or more mites are present per leaflet. If the number of predatory mites is at least one-half the number of two-spotted spider mites, treatment is not needed or can be delayed.
Consult the Louisiana Insect Pest Management Guide for a list of miticides and insecticides that can be used for controlling mites and insect in Louisiana strawberries. When spraying, be sure to check the pH of the water being used for spraying. The pH needs to be between 5.5 and 6.5 for optimum insecticide and miticide efficacy. Use of a buffering agent will help obtain the desired pH before adding pesticides to a solution. Ultrafine oil may be used with miticides or alone to enhance management. Complete coverage is essential for optimal control.
Spraying
Adequate spray coverage is essential to be successful with strawberries. Sprayers need to be calibrated to provide 50-100 gallons of water per acre at 60+ pounds of pressure to move the foliage. Each row needs three hollow-cone nozzles arranged to spray the underside of the foliage.
Labor Requirements
Strawberries are a labor-intensive operation. Growers need to have access to labor before ever attempting to go into the strawberry business. Generally, it requires one or two laborers per acre to lay plastic, plant, move row covers and take care of the early harvest of berries. However, when the berries reach the peak of harvest, it will require 3 or 4 individuals to keep an acre of the berries picked. Labor needs to be trained to plant strawberry plants correctly as well as pick and pack the fruit.
Bird Control
Several songbirds will feed on strawberries. Cedar waxwings and robins will feed on the ripe fruit. Yellow finches will feed on the seeds of the early fruit. Generally, bird damage is not a serious problem in large fields, because the feeding damage is spread out. However, bird damage can be a serious problem in small fields. Also, there are times when large flocks of birds hit a field and can cause quite a bit of damage.
Growers are warned that all songbirds are federally protected. In a situation of heavy bird damage, all the growers can do is to cover the berries with row covers during the day to prevent the birds from feeding on the berries. The use of propane guns is only effective with a small number of birds. With large number of birds feeding on berries, the birds quickly become used to the guns.
Wildlife Control
A strawberry planting can be easily damaged by wildlife. Deer and rabbits will eat the plants while coyotes, opossums and raccoons will eat the fruit. Electric fencing, 2-3 feet high has been used successfully to keep deer out of a field. Wires 6 and 12 inches from the ground need to be added to the fence to keep smaller animals out of the field.
The main problem with electric fencing is that the deer will break the fence several times before they learn to avoid the area. This means that the fence has to repair several times. Electric fences always require some attention. They are easily broken by tree limbs. The wires near the ground can be shorted out by tall grass.
Many times the smaller animals can go easily under the electric fence. The only control method successful for these animals is to remove them from the area.
Rodent Control
Rats and mice can be problems in strawberries. Many times they live under the plastic and feed on the ripe fruit. Cleaning up weedy areas near the field will reduce places for rodents to live. They can be controlled by the use of traps, glue boards and rodenticide baits in tamper-proof bait stations.