Chemical Sprout Control of Alaska Potatoes.

Abstract

POTATOES sprout in 11 to 15 weeks after harvest if placed in storage where 'temperatures average 40° F or above. Prior to this, growth regulating substances within the tubers prevent sprouting. If potatoes are stored at room temperature (70° F or higher) their dormant period will be shorter, although differences in varieties are observed. Varieties also differ in habit of sprout growth*. Some develop long sprouts that are relatively easy to remove. Even so, a new crop of sprouts will grow again from the same eyes if storage temperatures remain above 40oF for ten days or more. In addition to the expense of desprouting, potatoes lose weight and their market appeal. Potatoes can be and are stored at 30° to 36° for nearly a year with very little sprouting. Cold storage at this temperature range has some disadvantages. For example, starches are converted to sugar within the tubers. These sugars give cooked potatoes a sweet taste objectionable to some people. Potatoes with a high sugar content are not suitable for chipping and french frying. Sometimes they can be reconditioned by storing at 60° to 70° for a month or more but this warmer environment starts sprouting. Potatoes sprouting extensively in bins (as illustrated in Figure 1) cannot be ventilated properly because sprouts fill the air spaces between tubers. Lack of air movement through the bin causes a low oxygen supply and black heart or b1ack patches soon appear within tubers (Figure 2). Sprouting is costly to Alaskans in that it reduces the number of potatoes meeting U.S. No. 1 grade and therefore reduces farm income.Sprouting is costly to Alaskan's potato industry because it weakens Alaska's competitive position for summer markets. Summer im}:orts of dormant potatoes often capture a large segment of the Alaskan potato market. When these studies were begun, workers in other regions (2, 4, 5, 9) had demonstrated several methods of chemical sprout control. These methods included field spraying of tops, dusfng or dipping of tubers moving into storage, and gas treatment with volatile substances distributed within binned potatoes. Chemicals that had given the best control were methyl ester of naphthaleneacetic acid (MENA), indoleacetic acid (IA), maleic hydrazide (MH) and isopropyl N-(3 chlorophenyl) carbamate (CIPC). In other states MH has become so popular that it has been recently sprayed from an airplane ( 1) and CIPC has been released as an aerosol or vapor (6) within the storage. Some evidence has been presented (3) showing that healing of tender skins and healing of tuber bruises is delayed by sprout inhibitors. Unwashed potatoes frequently carry enough mud or wet soil into storage to inhibit good air movement through the bin. While washing prior to storage eliminates this particular problem, little is known about the storage characteristics of washed treated tubers (10). The objectives of these sh1dies were to learn (1) if sprout inhibitor chemicals used in other regions also inhibit Sf)routing of potatoes grown in Alaska's environment, (2) what effect snrout inhibitors have on yield and quality, (3) when and at what rate the chemical should be applied, (4) how sprout inhibitor treated potatoes store at different temperatures, (5) if washing fieldtreated potatoes prior to storage influences keeping ability or modifies sprout inhibitor action.