There are many excellent farm markets located throughout the Commonwealth that sell a wide variety of produce to consumers throughout the growing season. It is traditional here in Pennsylvania that in the late spring/early summer consumers are indeed anticipating the arrival of "new potatoes" or "B" size red potatoes at the local retail stands. These early potatoes command a high price and with the increasing popularity of specialty potatoes (different colored skins and flesh), growers are able to offer an increasing colorful display of potatoes to the consuming public.
In order to provide high quality, early potatoes for their markets, an increasing number of growers in Pennsylvania are using intensive production technology or plasticulture (plastic mulches, drip irrigation, fertigation, high tunnels, and row covers). Many growers are currently using this technology for other selected vegetable crops on their farms.
The use of plasticulture technology can provide:
- earlier production
- increase marketable yields
- improved quality of the product
In Pennsylvania we can have not only unpredictable growing conditions in the spring both in terms of temperatures and amount of precipitation, but also during the growing season, which can cause a delay in the maturity of the potato crop. The use of plasticulture helps ensure that a grower can have potatoes for the early market. The quality of the potatoes can also be affected by too much or too little water during the growing season.
The benefits of using plastic mulch, drip irrigation, and row covers has been well documented in both the research literature and popular press, and is an accepted practice for the production of many vegetable crops, not only in Pennsylvania, but around the United States and the world. The primary benefit of using plasticulture for potatoes is earlier production, greater yields, and higher quality.
Obvious advantages of plasticulture are:
- plastic mulches warm the soil up earlier in the spring which in turn hastens the emergence and development of the potato plant and prevents weed growth in the row
- drip irrigation in conjunction with the plastic mulches offer excellent control of soil moisture and the ability to fertigate
- elimination of hilling
- the potential reduction in disease pressure as well as the opportunity for insect management
Soil temperatures taken in May using a hand held soil thermometer at noontime under a clear sky are typical of those experienced in constant monitoring. The ambient air temperature was 74oF. The soil temperature was measured at a 4-inch depth on the raised beds both with and without plastic mulch and with and without row covers.
The soil temperatures for the raised beds without row covers were:
- red mulch 72oF,
- black mulch 72oF
- metalized silver mulch 69oF
- no mulch 71oF.
Soil temperatures on raised beds under row covers were:
- red mulch 78oF,
- black mulch 80oF
- metalized silver mulch 73oF
- no mulch 77oF.
This was a consistent trend and will continue until the plant canopy covers the surface of the raised bed at which time the temperatures under the mulch even out. The addition of row covers clearly increased soil temperatures. Faster emergence and increased growth of potato varieties grown under row covers has been observed each year. For potatoes grown without row covers, the growth of the potato plants on the red and black mulch were equal while the metalized silver mulch was slightly behind and no mulch was much further behind. Under row covers, emergence and growth of potatoes under red and black mulch were again equal, with silver mulch slightly behind and then even further behind no mulch.
The following potato varieties have been used in the plasticulture system:
- Keuka Gold (a light yellow flesh with white skin)
- Dark Red Norland (a white flesh with red skin)
- Eva (a white flesh with a bright white skin)
- Michigan Purple (a bright white flesh with a purple skin color)
- Red Pearl (a white flesh with a red skin producing 71% B size potatoes)
- Adirondack Blue (a blue flesh with a dark blue skin)
Dark Red Norland is a very early maturing variety with a relatively small plant canopy, Keuka Gold, Michigan Purple, Adirondack Blue, Red Pearl, and Eva are later maturing varieties and have larger plant canopies.
The plastic mulch/drip tape applicator used in vegetable production is also used for potatoes. The raised beds are generally 4-inches high and 30-inches wide with the drip tape buried 3 inches deep in the center of the bed. The Drip tape used is 8 mil-thick, has a 12-inch spacing between the emitter openings and a flow rate of 0.450 GPM/100 feet of row. Seedpieces can be hand-planted using a bulb setter to make two rows of holes spaced 18 inches between the rows with the holes spaced 8-inches apart in the rows on the 30 inch wide raised beds. This would be for very small plantings.
The potatoes are planted in double rows 18 inches apart with 12 inches in row, using a water wheel planter without water application at the time of planting the potato seedpiece, as is done with vegetable transplants. It is important to have adequate soil moisture prior to making the beds and applying the plastic mulch and drip irrigation tape, to ensure that the hole made by the waterwheel transplanter will not collapse before the seedpiece can be placed in the hole. We did develop in collaboration with colleagues in the Department of Agricultural and Biological Engineering a transplanter that utilizes cone-shaped dibbles that punch holes in the plastic bed, and can make holes 4 across, 2 across, or 1 depending on the crop, and in-row spacings (from 6 to 24 inches) depending on the crop.
Prior to making the beds and applying the plastic mulch and drip irrigation tape, fertilizer can be broadcast on the field. An example used in our plantings is for 450 lbs/acre of 34-0-0, 500 lbs/acre of 0-10-10 and 500 lbs/acre of 0-20-10 to be broadcast evenly across the field.
Spacing between the mulched beds is 6 feet. Though the distance between the mulched beds could be decreased to 5 feet apart, the plant canopies of the potatoes will quickly cover the space between the rows and can limit air circulation that is needed for disease control. Typar, a floating row cover material, is applied once the potato seedpieces are planted.
Admire can be injected through the drip irrigation system for control of some insect pests, such as the Colorado potato beetle and then standard pest management practices can utilized the remainder of the growing season. On a side note of interest, counting was done on Colorado potato beetle adults found on the different plastic mulches and bare ground the end of May: black mulch-94 beetles, red mulch-54 beetles, no mulch-36 beetles and silver mulch- 13 beetles.
The potatoes are routinely checked for development, and when the tubers are nearly marketable size, the vines are killed using Diquat. The potatoes are dug using a double row level bed digger and then picked up by hand. We have used a single row digger, but found it is too difficult to get the whole 30-inch wide bed up the digger. Potatoes will be set right out on the edge of the bed. Harvest begins with Dark Red Norlands, then Michigan Purple, Red Pearl, Adirondack Blue, Kueka Gold and Eva. Although the plastic mulch and drip irrigation tape will travel up the digger chain, it is easier to remove the plastic mulch prior to digging. This is best accomplished by mowing the dead potato vines as close to the plastic as possible with a rotary mower and then loosen the soil along the edges of the plastic, and either remove it by hand or use a small retrieval unit that will make a small round bale of plastic.
All plastic mulches significantly increased total and marketable yields for all varieties compared to bare ground. Marketable yields for potatoes grown with plastic mulch as compared to bare ground were:
Dark Red Norland:
- Red-249 cwt.
- Metallized Silver-246 cwt.
- no mulch-173 cwt.
For Keuka Gold:
- Black-357 cwt.
- Red-372 cwt.
- Metallized Silver-364 cwt.
- no mulch 262 cwt.
- Black-325 cwt.
- Red-298 cwt.
- Metallized Silver-301 cwt.
- no mulch-182.
The same holds true for Michigan Purple, Red Pearl, and Adirondack Blue.
The increased yields more than pays for the additional cost of the plastic mulch and drip irrigation tape. Although metalized silver mulch with or without a row cover had the coolest soil temperatures and slowest plant growth of the three colored mulches, the final yields are equal and sometimes better than the red and black mulch. There doesn't seem to be a corresponding increase in yield associated with an increase in plant growth. The positive effect of the red and black mulches covered or uncovered on the emergence of the potato is probably do to an increase in the soil temperature. This goes back to the fact that the rate of emergence and growth of sprouts from the seedpiece once it is planted is mostly a function of the soil temperature.
It is important to remember that the bare ground potatoes also received drip irrigation so the yield response is mainly a result of the plastic mulch. Plastic mulch and drip irrigation should be used together to get the maximum benefit from the system. It is recommended that a good strong black plastic mulch 1 to 1.25 mil thick be used for the production of potatoes, since, if a plastic mulch lets any light through, the potatoes that are on the surface or partially exposed will green up and be render unmarketable.
High Tunnel Production
High tunnels are part of plasticulture technology and are used worldwide for the production of a wide array of horticultural crops. In Pennsylvania the use of high tunnels permits the earlier production of a number of vegetable crops such as tomatoes, peppers, eggplant, and leafy greens. The use of high tunnels allows the production of early potatoes and is especially profitable if grown/marketed in conjunction with fresh garden peas and pearl onions, which are used together for a tasty spring dish. The use of high tunnels can provide growers the opportunity to market early red potatoes or red, white, and blue for the 4th of July holiday.
The system of production is very similar to field production, except the equipment size is smaller. Plastic mulch, drip irrigation, and row covers are use inside the high tunnels. In a 17-foot wide high tunnel, 3-foot wide plastic mulch is used to make four small raised beds 18 inches wide and 3 inches high which are spaced 44 inches apart. A small 21 HP tractor and plastic laying machine is used to apply the 3-foot wide plastic mulch and drip irrigation tape. Application of the plastic mulch and drip irrigation tape is similar to field production.
In the high tunnel black or red plastic mulch are good choices, since we want to really warm the soil up. If the plastic mulch and drip irrigation tape could be applied the preceding fall, it could then be ready for an early spring planting.
A note of caution, rodents may be a problem if plastic mulch and drip irrigation are applied in the fall. If fall application is not possible, then the plastic mulch and drip irrigation tape can be applied as soon as it is possible to enter the high tunnel in the early spring.
Fertilizer can be broadcast in the high tunnel and pulled into the row or some can be broadcast and then fertigated. The rates would be similar to the field situation, although lesser amounts can be used since in a high tunnel a grower has complete control over soil moisture and fertilizer.
Potato varieties commonly used in the high tunnels:
- Red Pearl - a red-skin/white flesh that makes 71% B size potatoes from the Wisconsin Potato Breeding Program
- Eva - a white skin/white flesh from the Cornell Potato Breeding Program
- Michigan Purple - a purple skin/white flesh from Michigan State Potato Breeding Program.
These were chosen in order to have some red, white, and blue skinned potatoes for a "Patriot Potato Salad" for the 4th of July. In central Pennsylvania, the potatoes can be hand-planted in April (soil temperature reaches 50oF) on double-rows 13 inches apart, with the potatoes spaced 8 inches apart in the row. The row cover is placed over the plastic covered beds.
Note: the row cover will provide some protection from an unexpected freeze event but it is recommended that some source of portable backup heat is available to prevent the tops of the potatoes from being killed off.
Potatoes are irrigated as needed and no pesticides applied to the crop. The potatoes should be dug by hand in June and ready for the 4th of July market.
- Red Pearl yielded 120 lbs. of potatoes
- Eva yielded 100 lbs.
- Michigan Purple yielded 139 lbs.
There were less than 10 tubers in the entire tunnel that had any defects.
- Red Pearl yielded 375 tubers/30 plants or 12.5 tubers per plant.
- Eva yielded 112 tubers/30 plants or 4 tubers per plant
- Michigan Purple yielded 90 tubers/30 plants or 3 tubers per plant.
The skin colors were excellent on all varieties. To take advantage of the skin colors of the potatoes and the 4th of July holiday, an American flag (3' wide by 5' long) made of the potatoes was constructed to show how they could be promoted in a retail market. These potatoes lend themselves to marketing in small woven baskets, in attractive displays, in polybags, or plastic clamshells and can command a high price.
If a grower had a 17' by 96' high tunnel and grew four rows at the 13" double-row, 8-inch in-row spacing, the yields should be:
- Red Pearl - 1,104 lbs. of potatoes,
- Eva - 920 lbs.
- Michigan Purple - 1,278 lbs.
The price of specialty potatoes at the food stores, according to a chart presented by the National Potato Promotion Board is 86/lb. If advertised and promoted at local retail markets, $1.50 for 1.5lbs. could be a reasonable price to expect. If we use $1.50 for 1.5 lb. then the gross return for each of the varieties would be
- Red Pearl- $1,104,
- Eva- $920
- Michigan Purple- $1,278.
This is for an area of production that is only 0.037 of an acre.
Prepared by William Lamont, professor of Vegetable Crops