Rhubarb

Introduction

Rhubarb, genus Rheum, has a long history of medicinal use in Asia. Its use as a food crop appears to be much more recent, with widespread table use beginning in the 19th century. The leaves of the plant are toxic, but the fattened petioles are consumed most commonly in pies and other sweetened desserts, in beverages, and occasionally as a vegetable. Several species of Rheum exist, and modern culinary varieties were likely derived from crosses between some combination of these species. The genus Rheum is not closely related to other vegetable crops; it belongs to the family Polygonaceae, along with buckwheat and many weeds including sorrels and knotweeds.

Rhubarb is a perennial that requires a dormant winter period below 40ºF to stimulate vigorous spring growth. It grows most vigorously in cool conditions, and growth is suppressed at high temperatures (>90ºF). For this reason, rhubarb is adapted to Northern latitudes in the U.S. and Canada. Once established, a rhubarb planting can remain productive for 8-15 years. 

Types and Varieties

Rhubarb varieties are classified as red, green, or speckled (pink).  The market generally prefers red over green or speckled.

In New England, the most common variety grown is Macdonald, also known as Macdonald's Canadian Red or Macdonald Crimson. This cultivar has large stalks and a vigorous and upright-growing habit, and is resistant to wilt and root rot. It is probably the most common variety available.  It is excellent for pies, canning, and freezing.  It can have medium to heavy seed stalk production.  At the beginning of the harvest season, late May, the petioles may be a deep red but will lose some or all of their color as the weather warms and as harvest extends through June into early July. 

Red types:  Crimson (may also be called Crimson Cherry, Crimson Red, or Crimson Wine). This is reportedly the only variety of consequence in Oregon but is reported to do well in New England. It produces brightly colored red stalks with the unique characteristic of being red throughout.  Other vigorous red varieties include Valentine and Cherry Red.

Speckled types (pink):  Victoria produces large stalks of excellent quality, long, round with smooth ribs. It develops pink speckling on a light green stalk with the pink color being more intense at the bottom of the stalk, fading to a solid green near the top. Victoria is commonly used for forcing.  Strawberry is very similar to Victoria, and may be the same variety. German Wine is similar to Victoria but slightly more vigorous and more intense in color, typically with a darker pink speckling on a green stem.

Green types:   Riverside Giant is a cold-hardy, vigorous producer with large diameter, long, green stalks.

Soil Fertility

Plant Nutrient Recommendatino According to Soil Test Results for Rhubarb
Soil Test Results Nitrogen (N) LBS per Acre
 
Phosphorus (P) Lbs per Acre Potassium (K) Lbs per Acre
Very Low Low Optimum Above Optimum Very Low Low Optimum Above Optimum
Planting Year
Broadcast and incorporate before planting 150 75 50 25 0 150 100 50 0
Sidedress one month after growth starts 45 0 0 0 0 0 0 0 0
Established Plantings
Before growth starts in spring 50 75 50 25 0 150 100 50 0
Before harvest 50 0 0 0 0 0 0 0 0
After harvest 50 0 0 0 0 0 0 0 0

Planting

The crown pieces are planted 3-6 inches deep, 2-3 feet apart, in rows about 4-6 feet apart or in a 4x4 foot grid to allow for cross cultivation. The most common spacing in Oregon is 2x6 foot although that may be tight for New England where 3x6 foot (2420 plants/acre) or 6x6 foot (1210 plants/acre) spacing is used. 

Field Culture

Irrigation is usually not necessary during the Spring/early Summer harvest of May/June/early July.  Maintain adequate soil moisture after the harvest season, to ensure good regrowth.  Soil type does not affect the amount of total water needed, but does dictate frequency of water application. Lighter soils need more frequent water applications, but less water applied per application.

Rhubarb requires a dormancy period of temperatures below 40ºF to break dormancy and stimulate the production of leaf petioles. Winter conditions in New England easily meet this requirement. When temperatures begin to exceed 45-50ºF, crown buds begin to develop. Early growth may be enhanced ten days to two weeks by the use of clear plastic row covers which may be applied in early February. Allow sufficient slack for stalk growth. 

Harvest and Storage

Harvest may start as early as mid-May. When petioles are of sufficient size for the market, they are pulled, not cut, from the plant.  For fresh market a small amount (1/4 inch) of leaf tissue is usually left attached to the petiole and the basal end is not trimmed.  For processing, all leaf tissue is trimmed from the petiole.

Stalks should not be pulled during the first year of growth. Stalk color is best after the field is 2-3 years old. Plants should not be over-pulled at any time, as a certain amount of foliage is required for the development of the present crop as well as next year's crop. At the end of petiole harvest (late June/early July) new shoots will emerge. These will provide the reserves for the following year's crop. Yields of rhubarb depend on the number of pickings, and the age and condition of the field but should yield an average of 6 tons per acre (600 20 lb cartons).  A well-maintained field may remain productive for 15 or more years. 

Store at 32ºF and 95-100% relative humidity. Fresh rhubarb stalks in good condition can be stored 2-4 weeks at 32ºF and high relative humidity. Rhubarb can be hydro-cooled or air-cooled, and the temperature of the stalks should reach 32 or 33ºF within 1 day of harvest. If not cooled properly, there is danger of heating and mold growth.  Moisture loss in storage will be much less if the bunched or loose stalks are packed in crates lined with perforated polyethylene film.

Disease

Leafspots and stalk rot diseases can be problematic following cool wet springs. Since both diseases overwinter in infected plant tissue, good sanitation practice should control most of the disease problems. Remove and dispose of infected plant tissue during the smmer and after first frost. Improved growing conditions may help minimize disease. Fertilize plant as growthbegins in the spring. Purchase disease free plant and remove dead foliage in the fall. 

copper oxychloride plus copper hydroxide (Badge X2OG): 1.0 to 2.25 lbs/A; PHI 0d, REI 48h, Group M1. Begin appication when disease first appears or when conditions favor disease.

Weed Control

Please note that this is a list of the registered herbicides for rhubarb in the Northeast, but that there is no specific crop safety data or efficacy data available for these products on rhubarb in our region. Always use caution when using new products until you have a sense on how they will perform in your field conditions on your crop.

 

Herbicides Used Preemergence, before weeds germinate

prometryn (Caparol 4L):  PHI 40d, REI 12h, Group 5. Make a single broadcast application to established rhubarb when plants are dormant, before leaves have emerged from the crown. Apply 2.0-3.2 pt/A on coarse-textured soils and 3.2-4.0 pt/A on fine-textured soils. Apply in a minimum of 20 gallons of water per acre. Within the rate ranges given, use the lower rate on relatively coarse-textured soils and soils low in organic matter; use the higher specified rate on relatively fine-textured soils and soils high in organic matter.

s-metolachlor (Dual Magnum): PHI 62d, REI 12h, Group 15.  Apply as a broadcast spray to soil surface in early spring prior to crop emergence. See label for specific rates on different soil types and organic matter content (0.67 to 1.33 pt/A). Will not control emerged weeds.

 

Herbicides Used for Pre- and Postemergence

halosulfuron (Sandea): PHI 60d, REI 12h, Group 2. Apply a single broadcast treatment of 0.5 to 1 oz/A in a minimum of 15 gal of water per acre to dormant rhubarb. The timing of the application should be as late as possible, or just prior to the breaking of rhubarb dormancy. Sandea may cause significant crop stunting. It is recommended that the user begin with a the lower rate to determine potential sensitivity to its use along with speed and degree of recovery. Provides both preemergence and postemergence control of many weed species, such as nutsedge and many broadleaf weeds. See the label for other precautions and a list of weeds controlled. For best results use a NIS if labeled weeds are emerged.

linuron (Lorox DF): REI 24h, Group 5. Apply as a single application of up to 3 lb/A as a dormant application (before leaves emerge from the crown). Make application as a broadcast or banded over-the-row treatment. Do not use on soils with less than 1% organic matter. Preemergence can control annual weeds as they germinate. Postemergence can control up to 2 inch tall annual grasses and up to 6 inch tall broadleaf weeds. See label for list of susceptible weeds.

mesotrione (Callisto):  PHI 21d, REI 12h,  Group 27.  Can make a single application of up to 6 fl oz/A to dormant rhubarb (established beds only) prior to crop emergence. Applications to rhubarb that is not dormant may result in a temporary bleaching symptomology. Rainfall or irrigation after the Callisto Herbicide application may increase the risk of injury to emerging rhubarb. If weeds are emerged at the time of application it is recommended to add an adjuvant (crop oil at 1% v/v or NIS at 0.25% v/v).

quinclorac (QuinStar 4L): PHI 30, REI 12h, Group 4. Not registered in VT. Apply up to 12.6 fl oz/A as a foliar application. A second application may be made at least 30 days later. A crop oil concentrate at a rate of 2 pints per acre may be included in the spray mixture. Crop oil can cause injury if used under hot and humid conditions (do not use if temp (F) + humidity exceeds 150). May control field bindweed, hedge bindweed and Canada thistle. Do not apply to stressed crop or injury may occur. Do not plant any other crop other than Spring or Winter wheat or grain sorghum for 10 months following application. For alfalfa, clover, dry beans, flax, peas, lentils, safflower, Solanaceous family crops (and other sensitive species listed in PRODUCT INFORMATION section of label) do not replant for 24 months and conduct a bioassay prior to planting any of these crops.

 

Herbicides Used Postemergence, after weeds germinate

clethodim (Select Max): PHI 30d, 24hr REI, Group 1.  Will control grass weeds only. Apply to actively growing grasses.  See label for rate selection.  Up to 4 applications permitted of 9 to 16 oz/A per application, minimum 14-days between applications, not to exceed 64 oz/A per year.  Add 0.25% v:v nonionic surfactant (1 qt per 100 gal of spray).  Can also be used as a spot-spray by mixing 1/3-2/3% (0.44 to 0.85 oz per gallon) Select Max and 0.25% v:v nonionic surfactant (0.33 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.

fluazifop (Fusilade DX): PHI 14d, REI 12h, Group 1.  Will control grass weeds only.  Apply up to 16 fl oz/A per application, minimum 14 days between applications. Maximum of 2 application permitted (not to exceed 32 oz/A per year).  Apply to actively growing grasses (see product label for susceptible stage). Add either crop oil concentrate (0.5-1%, 0.5-1 gallon per 100 gallons of spray) or nonionic surfactant (0.25-0.5%, 1-2 qt per 100 gal of spray).

sethoxydim (Poast): PHI 30d, REI 12h, Group 1.  Will control grass weeds only.  Apply to actively growing grasses (see product label for susceptible stage).  Maximum 1.5 pt/A per application, minimum 14-days between applications.  Do not exceed 3 pt/A per year. Use with crop oil concentrate (2.0 pt/A) or methylated seed oil (1.5 pt/A).  Note that crop oil can cause injury under hot and humid conditions.  Can also be used as a spot-spray by mixing 1-1.5% (1.3 to 1.9 oz per gallon) Poast and 1% v:v crop oil concentrate (1.3 oz per gallon).  Spray to wet, but do not allow runoff of spray solution.