Desiccant and defoliating spray composition for leguminous plants

Spray oil compositions capable of defoliating and/or desiccating the foliage of leguminous plants so as to facilitate the harvesting thereof are disclosed. The parameter of properties constituent oils must have to provide these effects is given.

FIELD OF THE INVENTION 
The present invention is generally concerned with the defoliation and/or 
dessication of legume foliage using mineral spray oils for facilitating 
mechanical harvesting and is more particularly concerned with petroleum 
compositions capable of effecting such results. 
BACKGROUND OF THE INVENTION 
The presence of moisture on the leaves of legumes caused by rainfall, dew 
of guttation makes combined harvesting of the crop difficult. This problem 
is particularly serious with Black-eye pea (Vigna sinensis). The Black-eye 
pea plant forms a canopy which remains green and healthy even up to the 
time the mature yellow and/or dry pods are ready for harvesting. The 
presence of moisture on the living plant makes mechanical harvesting 
difficult and crop losses are particularly heavy. Defoliation and/or 
desiccation of the foliage using mineral spray oils would preclude 
moisture formation on the leaves thus facilitating mechanical harvesting 
of the crop. 
STATEMENT OF THE PRIOR ART 
Defoliation and/or desiccation with chemicals have been in practice for a 
long period of time on crops such as bean, cotton, corn, sorghum and so 
on. There is no sharp line of demarcation between defoliants and 
desiccants, and, in fact, their effects overlap. High application rates of 
defoliants may give rise to considerable desiccation, while low rates of 
desiccants may cause a considerable amount of defoliation, especially when 
used on legumes. Defoliation is accelerated leaf-fall, and requires the 
functioning of living tissues at the leaf base. Both internal and external 
factors effect this phenomenon. The principal internal factor is hormones 
or auxins, the gradient across the leaf base which regulates leaf fall. 
The main external factors are temperature and moisture. Defoliation is 
favored by relatively high temperature and moderate leaf moisture. 
Defoliants appear to act through a mild general injury to both the lamina 
and petiole. Conversely, desiccation is the chemically accelerated drying 
of plants or plants parts, and does not require active functioning on the 
part of the plant. In fact, desiccants are essentially contact herbicides 
such as herbicidal oils. During desiccation, the role of the plant tissue 
appears to be completely passive. The tissue contacted by the desiccant 
rapidly loses moisture and dies. Contigous tissues die somewhat later, but 
remote tissues remain unaffected. Usually all aerial parts except seeds 
are killed by the desiccant, and their effects are similar, if not 
identical, to those of contact herbicides. The degree of injury to some 
extent determines the rate of desiccation. Environmental factors, 
especially the relative humidity, are most influential. When the relative 
humidity is low, desiccation is rapid, and, when high, it is slow. 
SUMMARY OF THE INVENTION 
In accordance with the invention it has been found that petroleum 
compositions characterized by a viscosity range at 100.degree. F. of 
between 34 and 110 SUS, an aromatic content of between 18 and 55 percent, 
a boiling range of about 180.degree. C. with initial boiling temperature 
of between 180.degree. and 420.degree. C., a maximum unsulfonated residue 
of 85 percent, a surface tension of between 24 and 28 dines per centimeter 
at 30 C and a Harkins spreading coefficient for one minute of between 19 
and 28, and for 30 minutes of between about 17 and 31, possess outstanding 
defoliating and/or desiccating properties for the foliage of leguminous 
plants. To improve spreading characteristics of the oils, from 0.1 to 1.0 
weight percent of a non-ionic surfactants such as Sponto AC 60 may be 
added. From 56 to 560 liters per hectare of the composition is applied to 
the foliage of the plants by sprayers. 
The preferred petroleum oils tested and shown to have defoliant/desiccant 
properties when sprayed on Blackeye pea foliage are two gas oils, two lube 
oil base stocks and two relatively light (low boiling range) oils (Ref. 
Table I). These spray oils, especially the Heavy Gas Oil, caused moderate 
to severe desiccation and defoliation when applied to the Black-eye pea 
foliage. The results of the trials are given in Example I. These oils have 
the advantage over most chemical compounds used as defoliants and 
desiccant of being less costly and of not leaving toxic residues on the 
harvest, plant remains and soil as do chemicals. 
The invention is further illustrated in nonlimiting fashion by the 
following examples.

EXAMPLE I 
Three trials (Nos. 14/76, 26/76 & 3/77) were conducted to evaluate the 
defoliant/desiccant properties of spray oils of varying properties. The 
Black-eye pea (Vigna sinesis) plants used in the trial were grown in 
plastic pots; 16.5 cm diameter and 17.8 cm deep, containing a growing 
medium of vermiculite, peatmoss, sand and charcoal mixture. The growing 
seedlings received Shive's nutrient solution at intervals during their 
entire period of growth. A randomised block design was used with the 
treatments replicated three times in three blocks. In Trial Nos. 14/76 and 
3/77, the spray oils were applied to the foliage of fruting plants, while 
in Trial 26/76, the spray oils were applied before the plants commenced 
fruiting. In Trial No. 14/76, the potted seedlings were taken from the 
greenhouse and placed in the open 7 days before they were sprayed, while 
in the other trials, the potted seedlings remained the entire trial period 
in the greenhouse. The leaf-burn caused by the oils in Trial No. 14/76 
tended to be blotchy in appearance due to minimal spreading of the oils on 
the leaf surfaces. The spreading coefficient of the oils used in Trial 
Nos. 26/76 and 3/77 were improved by the addition of Sponto AC 60 an oil 
soluble emulsifier for agricultural spray oils (Ref. Table II). The spray 
oils were applied with a fixed artist's spray brush at the rate of 5 ml 
per pot of 3 plants; this rate of application is equivalent to about 560 
liters per hectare, and is about 10 times the recommended dosage of 
Stoddard Solvent used as a herbicide in cotton and soybean. The oils were 
applied as a blanket spray to the plants. In Trial No. 14/76 the plants 
were shielded to preclude spray drift, while in Trial Nos. 26/76 and 3/77 
the potted plants were placed on a spinning platter (19 revs/minute) 
housed in a chamber, and the oils applied from above, 80 cm from the 
foliage. The extent of leaf-burn and leaf-fall was assessed over a period 
of about two weeks. The mean data are shown in Tables III to IX. 
The lube oil basestocks used are the light and the heavy dewaxed refined 
waxy distillates (