Protection of plants against freeze damage by treatment with about 0.05 to about 2.5 wt. % aqueous solution of water soluble nonionic surface active polyoxyethylenated polyoxypropylene block copolymers, optionally also containing urea.

This invention relates to compositions, methods and apparatus for plant 
cryoprotection, i.e. for increasing the resistance of plants to damage by 
low, especially freezing, temperatures. 
Freezing temperatures have always been a major cause of temporary or 
permanent damage to plants and plant parts including seedlings, shoots, 
trunks, bark, growing points, buds, leaves, flowers, fruits and/or 
vegetables. Numerous types of approaches have been devised for the purpose 
of inhibiting such plant damage, including laborious, time-consuming and 
costly development of hardy plant species, mechanical protection such as 
coating and bagging, and the like. Accepted methods of frost control using 
wind machines, heaters and/or irrigation involve a high capital cost 
followed by increasing running costs of rising fuel prices. Treatment, 
e.g. spraying, of the plant with a suitable cryoprotectant chemical prior 
to exposure to freezing conditions would appear to constitute a simple and 
relatively inexpensive solution to this problem. Plant growth inhibitors 
and other chemicals which delay growth and/or bud development in the 
spring and thereby avoid injury caused by spring freezes have generally 
been found to introduce side effects and/or reduce crop yields. Other 
types of chemicals have been experimented with for plant cryoprotection 
including polyvinyl pyrrolidone, glycerol, ethylene glycol, and the 
dodecyl ether of polyethylene glycol (DEPEG). However, as stated in 
"Analysis and Improvement of Plant Cold Hardness" by Olien and Smith, CRC 
Press, Inc., Boca Raton, Florida (1981), page 188, "Despite numerous 
attempts to increase hardiness with chemicals, few if any practical 
applications have resulted to date . . . The search for chemicals which 
will increase hardiness continues, however, and may well lead to 
commercially acceptable methods of reducing field injury." 
It is an object of this invention to provide such a chemical. Another 
object of this invention is the provision of a plant cryoprotectant 
chemical which will not be subject to one or more of the above 
disadvantages. Still another object of this invention is the provision of 
a plant cryoprotectant chemical which is non-phytotoxic, non-toxic, 
biodegradable and environmentally acceptable. Yet another object of this 
invention is the provision of compositions, methods and apparatus for 
employing such chemical for cryoprotection, i.e. increasing the resistance 
of plants to damage by low, especially freezing, temperatures. Other 
objects and advantages will appear as the description proceeds. 
The attainment of one or more of the above objects is made possible by this 
invention which includes a method of increasing the resistance of plants 
to damage by freezing conditions comprising applying to the plant surfaces 
prior to exposure to such conditions an aqueous solution containing, 
approximately by weight and as an essential active cryoprotectant 
component, 0.05% to 2.5% of a water soluble nonionic surface active 
polyoxyethylenated polyoxypropylene block copolymer having a molecular 
weight of about 2,000 to about 7,000 and a molar ratio of propylene 
oxide:ethylene oxide of about 2.5:1 to about 0.7:1. 
The invention also includes the provision of the above-defined aqueous 
solutions and plant spray apparatus containing same, for plant 
cryoprotectant purposes. 
The invention further includes the provision of an aqueous plant 
cryoprotectant solution in which the solute consists essentially of, 
approximately by weight, 0.05% to 2.5%, preferably about 0.1 to about 
0.5%, more preferably about 0.25%, of a water soluble nonionic surface 
active polyoxyethylenated polyoxypropylene block copolymer having a 
molecular weight of about 2,000 to about 7,000, preferably about 4,000 to 
about 5,000 and a molar ratio of propylene oxide:ethylene oxide 
(Pr.O.:E.O.) of about 2.5:1 to about 0.7:1, preferably about 1:1, and 0 to 
2, preferably about 0.5 to about 2, parts of urea per part of said 
copolymer, in addition to the method of treating plants therewith and 
plant spray apparatus containing same. 
The above-defined block copolymer is a well known type of nonionic 
surfactant commonly made by condensing the requisite number of water 
solubilizing moles of ethylene oxide (E.O.) with a polypropyleneglycol 
hydrophobe nucleus of requisite molecular weight. These surfactants have 
good wetting, dispersing, emulsifying, and detergency properties combined 
with low foam. They have been used as detergent-active agents, and in 
agriculture for improving wetting properties and for solubilizing, 
dispersing or emulsifying other functionally active components such as 
pesticides, growth regulators, fertilizers and the like, i.e. as 
secondary, assistant or auxiliary agents and not as the sole or major 
active component. For any given polyoxypropylene hydrophobe, the water 
solubility of the copolymer varies directly with the percentage of 
polyoxyethylene combined therewith, i.e. the molar ratio E.O.:Pr.O., or 
inversely with the molar ratio Pr.O.:E.O. All the copolymers operative 
herein are water soluble at the defined concentrations at ambient 
temperatures to yield generally clear solutions, although it will be 
understood that the terms "water soluble", and "solution" as employed 
herein include products which are colloidal, or readily water-dispersible 
or -emulsifiable and the resulting aqueous "solutions" containing them. 
The nonionic surfactant copolymers suitable for use in this invention are 
commercially available. The Monolan products of Diamond Shamrock 
Corporation, described in its Product Bulletin entitled "Monolan Series", 
1982 are representative, ranging from clear liquids to pastes or 
semi-solids with increasing molecular weight. Preferred among such 
products are Monolan 2800, a clear liquid with a molecular weight (MW) of 
about 2800 based on a 1750 MW polyoxypropylene hydrophobe (Pr.O.:E.E. of 
1.67:1); and Monolan 6400, a semi-solid of about 5800 MW based on a 3200 
MW Pr.O. hydrophobe (Pr.O.:E.O. of 1.22:1). Most preferred is Monolan 
4500, a semi-solid of about 4600 MW based on a 2200 MW Pr.O. hydrophobe 
(Pr.O.:E.O. of about 0.92:1 or about 1:1). Nonionic surfactant copolymers 
operative herein are also available as Pluronic products of 
BASF-Wyandotte. 
According to a further feature of this invention, it has been found that 
even better protection against freezing conditions, often with faster 
absorption by the plant, is attainable when the above-described copolymer 
solution of this invention further contains some urea, preferably about 
0.5 to about 2 parts, more preferably about 1 part, of urea per part by 
weight of the copolymer. The urea should be substantially pure, preferably 
crystalline, containing little or no biuret, i.e. less than about 0.5 wt. 
% of biuret. 
The solutions employed according to this invention may be made and supplied 
to the user in more concentrated form, e.g. from about 5 wt. % up to about 
60 wt. % or more aqueous solutions of the copolymer and desirably urea, to 
be suitably diluted with water prior to application to the plant. If the 
solution is not to be used promptly following its formation, it should be 
stored in opaque containers, e.g. amber colored glass or the like, to 
prevent deterioration by exposure of the copolymer to sunlight. In some 
instances, as when the copolymer is a paste, gum or other semi-solid, and 
therefore not as readily or quickly soluble as desired, the copolymer and 
optional urea may be provided in the form of a concentrate in a 
water-miscible polyhydric alcohol such as glycerin, propylene glycol, 
ethylene glycol, polypropylene glycol and/or polyethylene glycol. Such 
concentrates may contain any desired porportion of the copolymer, such as 
about 5 to about 60 wt. % or more, preferably about 30 to about 50 wt. %, 
with optional urea, to be stored in opaque containers and suitably diluted 
with water prior to use. 
It is highly preferred that the copolymer solutions of this invention be 
devoid of (i.e. any significant amounts of) organic or inorganic 
fertilizers, pesticides, plant hormones and growth regulators, other 
polymers and coating materials, and the like since it has been found that 
they diminish or destroy cyroprotective and other desired and desirable 
effects and properties of this invention. Further, copolymer 
concentrations of about 3 wt. % or more have for some unknown reason been 
found to similarly diminish or eliminate the desired cryoprotective 
effects. Additionally, it was found that solutions prepared from the 
above-described concentrates of the copolymer in a water-miscible 
polyhydric alcohol were substantially more slowly absorbed by the plants 
than solutions prepared from concentrates devoid of the polyhydric 
alcohol. Such polyhydric alcohol-containing solutions must therefore be 
applidd to the plants at a relatively longer lead-time, i.e. at least 
about 36 hours prior to exposure of the treated plants to freezing 
conditions. Obviously, solutions which are more quickly absorbed by the 
plants are to be preferred since they may be applied in emergency 
situations, e.g. involving brief prior warning of impending freeze-ups. 
Although the copolymer solutions of this invention may be applied to the 
plants immediately prior to exposure to freezing conditions to obtain 
cryoprotective results, it is preferred for optimal results to apply the 
solutions at least about 6 hours, preferably at least about 24 hours, 
prior to such exposure to permit more complete absorption of the 
solutions. For similar reasons, the treated portions of the plants should 
not be watered or sprayed with any other liquid medium for at least about 
6 hours, preferably at least about 24 hours, following the treatment. Any 
such inadvertant watering or spraying, or rain, during such initial period 
of absorption may necessitate repetition of the copolymer treatment of 
this invention. The cryoprotective effects are retained up to about 30 
days or more after treatment with these copolymer solutions, as evidenced 
by significant reductions in bark and stem splitting, defoliation, foliage 
burn, fruit damage or drop, yellowing, dessication, and other plant damage 
and mortality when the treated plants are subjected to freezing 
conditions. 
Any suitable plant spray apparatus suitable for spraying aqueous solutions 
may be employed. An example of such apparatus is a compressed air atomizer 
such as the Chromist Spray Unit of Gelman Instrument. The plants to be 
treated are lightly but thoroughly sprayed, preferably on all their 
surfaces, short of "run-off". The plants may be in any of their various 
forms, e.g. seedlings, shrubs, bushes, vines, and trees in any stage of 
growth, and the application may be made day or night, at ambient warm, 
room or cold temperatures. 
The mechanism by which this invention achieves its desired cryoprotective 
effects is as yet not fully understood. It functions systemically 
following absorption of the copolymer solution applied to the plant 
surfaces. A plant response to the treatment has been recognized which 
indicates that significant translocation of the copolymer, or a derivative 
thereof, occurs in the treated plant following such absorption. More 
particularly, when young growing plants were sprayed with the copolymer 
solution of this invention and exposed to heavy freeze conditions one 
month later, the lower leaves which had been originally sprayed sustained 
significant damage whereas the upper newly grown parts of the plant (which 
were of course not directly sprayed) were protected from the frost and 
showed little or no damage. Another plant response to the treatment 
according to this invention has been noted, namely stimulation of plant 
growth relative to untreated plants. 
The following examples of certain embodiments of this invention are to be 
regarded as only illustrative and not limitative. All amounts and 
proportions referred to herein and in the appended claims are by weight, 
and temperatures are in degrees F., unless otherwise indicated. The PPC 
707 employed in the examples corresponds to the above-mentioned Monolan 
4500-polyoxypropylene (MW 2200)/polyoxyethylene, MW 4600.

EXAMPLE 1 
A. To 100 parts of water (preferably distilled) at room temperature, e.g. 
50.degree.-80.degree. F., in a magnetic stirrer are added 2.5 parts of PPC 
707 and the mixture stirred to a water-clear solution concentrate. If not 
to be used immediately, the concentrate is stored in an opaque container, 
e.g. amber-colored glass vessel, to prevent deterioration by sunlight. For 
application to plants, the concentrate is extended with tap water to 1,000 
parts, i.e. yielding an 0.25% by weight aqueous solution of the active PPC 
707, which solution is loaded into a Chromist compressed air atomizer 
spray apparatus (Gelman Instrument) for spraying on plant surfaces 
thoroughly but short of run-off. 
B. The procedure of preceding paragraph A is repeated, except that 2.5 
parts of urea (substantially pure) are initially added with the 2.5 parts 
of PPC 707 to the magnetic stirrer. 
C. The procedure of paragraph A is repeated except that the magnetic 
stirrer contains 2.5 parts of (a) polypropylene glycol (M.W. 600), or (b) 
glycerin or (c) Carbowax 60 (polyethylene glycol) instead of 100 parts of 
water. 
In the following examples, the procedure of Example 1A was followed in 
making the plant cryoprotectant solution and treating the plant surfaces 
therewith, unless otherwise indicated. 
EXAMPLE 2 
TEST IN GEORGIA 
This test was conducted on Patio and beefsteak tomato plants and pepper 
plants in a field in Colquitt County, Georgia, initiated in early fall 
with PPC 707 and two other chemical treatment solutions for comparison. 
Different sets of plants were sprayed, beginning about a week after 
planting, about every week from 5 weeks. About 21/2 weeks after planting, 
all plants were fertilized and dusted with 5% Malathion dust. A month 
after first spraying, all plants were growing well, tomato plants had 
blossoms and small green tomatoes. Three days after the last spraying, the 
plants were subjected to heavy frost conditions in a three day period. 
Nine days after the last spraying, the temperature in the field dropped to 
22.degree. F. for several hours overnight. 
Plants treated with PPC 707 appeared most resistant, with only a few burned 
spots on the bottoms of leaves. Most plants survived, with blooms and 
vegetables in good condition. 
Plants treated with Kingfish liquid fertilizer, a hydrolyzed fish protein 
claimed to have cryoprotectant properties, at the same 0.25% 
concentration, were least resistant to freezing conditions, being 
completely burned and eventually dying. 
Plants treated with a solution containing 0.25% of each of PPC 707 and 
Kingfish liquid fertilizer showed intermediate resistance to freezing 
conditions, most plants being burned and yellow but not dead. 
It was noted that the growing plants sprayed with PPC 707 about a month 
before the heavy freeze showed damage to the lower leaves which had been 
originally sprayed whereas the upper, newly grown parts of the plants 
(which had not been sprayed) were resistant to the freeze conditions, 
indicating systemic transmigration of the cryoprotectant chemical. This 
test further indicated that the cryoprotectant effect of the PPC 707 
treatment lasted for at least about 11/2 months. 
The following tests were conducted in the vicinity of Vero Beach, Indian 
River County, Florida. 
EXAMPLE 2 
Comparative Citrus Test 
Seedlings of the Mandarin orange Cleopatra, growing in soilless culture of 
vermiculite, peat and perlite were exposed to low temperatures of 
40.degree. F. to 50.degree. F. night time for a week in midwinter to 
harden them off so that they were more resistant to freeze damage. 
Different sets of the plants were then sprayed in the open with 0.25% 
solutions of PPC 707 and of the other solutions listed in Table 3 below, 
following the procedure of Example 1A. Eight days later, early morning 
temperatures were about 30.degree. F. for 3.5 hours, with sporadic winds 
of 5 to 15 mph. Nine days after spraying, the plants were subjected to 
similar winds and heavy freeze conditions, the official weather bureau 
records for Indian River County showing the following temperatures for the 
night of the ninth day and the morning of the tenth day. 
TABLE 1 
______________________________________ 
8 P.M. 
9 P.M. 10 P.M. 11 P.M. 12 P.M. 
1 A.M. 
______________________________________ 
30.degree. F. 
29.degree. F. 
28.degree. F. 
28.degree. F. 
28.degree. F. 
26.degree. F. 
______________________________________ 
2 A.M. 
3 A.M. 4 A.M. 5 A.M. 6 A.M. 7 A.M. 
______________________________________ 
26.degree. F. 
24.degree. F. 
24.degree. F. 
24.degree. F. 
24.degree. F. 
24.degree. F. 
______________________________________ 
The treated plants were located about 2 miles from the weather recording 
station in an area about 2.degree. F. colder than those shown in Table 1. 
Fifteen days after being exposed to the above conditions, with temperatures 
about 40.degree. to 50.degree. F., the cryoprotectant antidefoliation 
effects of the several solutions were evaluated on to following scale. 
TABLE 2 
______________________________________ 
Rating Plant Symptoms 
______________________________________ 
0 plant completely dead 
1 severe defoliation 
2 70% defoliation 
3 50% defoliation 
4 30% defoliation 
5 20% defoliation 
6 15% defoliation 
7 10% defoliation 
8 5% defoliation 
9 2.5% defoliation 
10 total freeze resistance 
______________________________________ 
The results of the evaluation were as follows: 
The results of the evaluation were as follows: 
TABLE 3 
______________________________________ 
Chemical Rating 
______________________________________ 
Tween 60-polyoxyethylene (20) sorbitan monostearate 
1 
Teric 12A23B-dodecyl ether of polyethylene (23) glycol 
1 
Trycol 550 La1 8-dodecyl ether of polyethylene (9) 
1 
glycol 
Trycol La1 45J-hexadecyl ether of polyethylene (6) 
2 
glycol 
PPC 707-Polyoxypropylene (MW2200)/polyoxy- 
9 
ethylene, MW 4600 
PPC 708-Polyoxypropylene (MW1750)/polyoxy- 
8 
ethylene, MW 2800 
PPC 709-Polyoxypropylene (MW3200)/polyoxy- 
4 
ethylene, MW 5800 
Kingfish hydrolyzed fresh protein 
4 
______________________________________ 
EXAMPLE 3 
Rose Test 
In the same area, but only 2 days prior to the period recorded in Table 1 
above, 29 large rose plants of each of several varieties from Jackson and 
Perkins, all budded on Dr. Huey, were sprayed with PPC 707. Similar 
control plants were not sprayed. Following exposure to the freeze 
conditions described in Example 2, flower buds of all varieties were 
affected, but the control plants were severely defoliated in contrast to 
the sprayed plants which continued to grow well with no foliage burn. Ten 
days after said freeze conditions, the bark on the control plants split, 
but not on the sprayed plants. 
Tested plant varieties were Tribute, American, Pride, Snowfire, Oregold, 
Proud Land, Fragrant Cloud, Tropicana, Double Delight and Olympia. 
EXAMPLE 4 
Vegetable Test 
In the same area, but in the evening of the eighth day prior to the period 
recorded in Table 1 above, large sweet onion plant and Chinese cabbage 
plants were sprayed with PPC 707 at 50.degree. F. and 29% humidity, and 
irrigated during the next 3 days. These sprayed plants were not damaged by 
the freeze conditions described in Example 2. 
EXAMPLE 5 
Ornamental and Citrus Test 
In the same area and on the same day as the above Rose Test of Example 3, 
Carissa, Iothosporus, lily, springi fern, gardinia, geranium, navel 
orange, pink grapefruit and scheffelera plants were sprayed with PPC 707. 
Following exposure to the freeze conditions described in Example 2, only 
geranium plants and some types of the scheffelera showed injury, but none 
serious. All plants continued to grow and 2 young citrus plants broke out 
with new growth within 9 days of the freeze. 
EXAMPLE 6 
Citrus Test 
In the same area and on the same day as the above Rose Test, pink 
grapefruit trees 5 feet high, and citrus seedlings of variety Cleopatra 
and sour orange were sprayed with PPC 707. Similar control plants were not 
sprayed. 
Following exposure to the freeze conditions described in Example 2, tips of 
leaves on some of the young new growth on the large grapefruit trees, 
which had been fertilized and were in soft growth condition, showed slight 
leaf burn. The citrus seedlings were practically unaffected except a few 
leaf tips apparently from wind burn. 
Twenty -one days after the afore-described freeze conditions, another 
severe freeze occurred for a total of 14 hours, with temperatures down to 
22.degree. F., for most of the night. 
The tips of some of the young growth on the grapefruit trees were injured, 
but one week later, the control trees showed severe injury with 50% 
defoliation and 75% fruit drop, in contrast to the sprayed trees which 
surprisingly showed less than 10% defoliation and 10% fruit drop with no 
injury to undropped fruit. 
The citrus seedlings survived both freezes without serious injury and 
continued to grow well. 
EXAMPLE 7 
Additive Test on Tomatoes 
Different sets of tomato plants were sprayed with 0.25% solutions of PPC 
707 (Example 1A), PPC 707 with urea (Example 1B), with glycerin (Example 
1C(b)), and with Carbowax 60 (Example 1C(c)). The plants were subjected to 
freeze conditions 18 hours after spraying, with temperatures of 29.degree. 
F. for four hours. Plants treated with the PPC 707 and PPC 707/urea 
solutions were unaffected by the freeze, but plants treated with the PPC 
707/glycerin and PPC 707/Carbowax 60 solutions were killed, indicating 
that the glycerin and Carbowax 60 prevented absorption of an effective 
amount of the PPC 707 during the 18 hour period between spraying and 
freeze, and that longer prefreeze periods would be necessary. 
This test further indicates the sensitivity of the copolymers of this 
invention to other materials in the spray solutions. As described above, 
these copolymers are sensitive to salts. Initial tests on beans indicated 
that inclusion in the spray solution of low dosage of NPK water soluble 
fertilizer (Miracle Gro, 2 grams per quart) completely nullified the 
desired cryoprotectant results. This may explain the lack of recognition 
in the agriculture art of the cryoprotective properties of these 
copolymers which have hitherto not been employed as sole active functional 
agents on plants, trees, etc, 
This invention has been disclosed with respect to preferred embodiments, 
and it will be understood that various modifications and variations 
thereof obvious to those skilled in the art are to be included within the 
spirit and purview of this application and the scope of the appended 
claims.