The control of spider mites (Tetranychidae) on Musoid plants is
challenging in any large collection of ornamental plants. The
colonization of Musoid plants by spider mites normally begins on the
oldest or senescent leaves. This observation by the author was made on
Musa, Heliconia, and Calathea species at several plant collections in
the South Florida area over a period of many years. An Integrated Pest
Management (IPM) program can be initiated to substantially reduce
reliance on chemicals for the control of spider mites. This program is
not only ecologically sound, but is also very cost-effective.
Substantial savings are realized from reduced chemical purchases, and
skilled labor that is freed from constant spraying can be utilized in
other areas of the garden.
The onset of senescence (dying) - be it a single leaf, a branch, or
the entire plant - brings about a breakdown of protein to soluble amino
acids in the senescing tissue. This soluble nitrogen is translocated via
the phloem to sites of storage (seeds) or new growth (Hill 1980). Many
herbivorous insects are "flush feeders" that are adapted to
feed on this nutritious sap contained in new growth (Auerbach and Strong
1981). Spider mites are "senescence feeders" that tap into
this rich sap as it flows away from senescing tissue (White 1971).
Many different chemicals are used to control spider mites i.e.:
Aldicarb (1), Dicofol (2), Oxamyl (3), Dienochlor (4), and Fluvalinate
(5) [see footnotes]. These are all used with varying degrees of success
on plants in the ground as well as on containerized plants. Pesticides
are normally used on a rotational basis as chemical resistance becomes
evident. During the course of a year certain groups of plants may be
sprayed as many as eight times.
Pesticide use selects for pesticide resistance, and reduces the
efficacy of biological control agents, such as predatory insects and
fungi. This makes pest control increasingly difficult and costly. The
use of chlorinated hydrocarbons, organophosphate pesticides, and
fungicides has been shown to be followed by spectacular increases in the
abundance of phytophagous mites on plants sprayed (McCoy 1977). An
explanation for this phenomenon may be a reduction in biological control
agents or a change in the physiology of the food plant due to a sudden
increase in the concentration of available nitrogen in the tissues after
the use of these chemicals (Bartlett 1968, White 1984).
Another factor that may cause an increase in mites is water stress.
It has been suggested that drought is likely to increase the amount of
readily available and assimilable nitrogen in the tissues of the food
plant (White, 1974, 1984).
In spring 1988 the author implemented an IPM program for the control
of spider mites on Musoid plants. This included provision of adequate
water; plants were watered frequently as needed to prevent wilting.
Lower leaves (leaves that would turn yellow in a few weeks) on all
plants were removed on a regular basis. The objective in removing these
leaves was to decrease the amount of available nitrogen to the spider
mites.
After 2 years the program appears to be successful. The most any
group of Musoid plants in the program has been sprayed is twice per
year. Some have not required a single spraying. Removal of pre-senescent
leaves does not appear to cause undue stress to the plants. Growth
remains vigorous and flowering times seem consistent with pre-IPM times.
Fruiting by Musa species is not affected and many plants appear to be
more robust, although this is a subjective observation. All plants are
fertilized on a regular basis and that schedule is not altered to
supplement the loss of nitrogen due to leaf removal.
This IPM program for the control of spider mites on Musoid plants is
entering its third year. Not only are hundreds of dollars in labor and
chemical costs being saved, but an ecologically sound pest control
program is being implemented.
Such an IPM program is ideal for zoological parks. Musoid plants and
members of the Araceae are often not used in exhibits containing animals
because of their susceptibility to spider mites. Chemical control of
insect pests must be avoided around animals, especially ones as
sensitive as birds. The removal of pre-senescent leaves of certain plant
families may allow managers of animal exhibits to have more varied and
exotic plant displays. This practice along with other IPM techniques
should greatly assist horticulturists who are concerned about the
excessive use of chemicals and their impact on the environment.
(I) Temik. Union Carbide Corp., PO Box 1905, Salinas, California
93901
(2) Kelthane. Rohm and Haas Corp., Independence Mall street,
Philadelphia, Pa. 19105
(3) Vydate L. E.I. duPont de Nemours and Co. Inc., 1007 Market Street,
Wilmington De. 19898
(4) P. Sandoz Crop Protection Corp., 1300 East Touhz Ave., Des Plaines,
1ll. 60018
(5) Mavrik Aquaflow. Sandoz. Crop Protection Corp., 341 East Ohio
Street, Chicago, I11. 60611
References Cited:
Auerbach, Michael J. and Donald R. Strong (1981) Nutritional ecology
of Heliconia herbivores: Experiments with plant fertilization and
alternative hosts. Ecological Monographs 51(1): 63-83.
Bartlett, B,R, (1968) Outbreaks of two-spotted spider mites and
cotton aphids following pesticide treatment. 1. Pest stimulation vs.
natural enemy destruction as the cause of outbreaks. J. Econ. Ent. 61:
297-303
Hill, J. (1980) The remobilization of nutrients from leaves. J. Plant
Nutrit. 2: 407444.
McCoy, C.W. (1977) Resurgence of citrus rust mite populations
following applications of methidathion. J. Econ. Ent. 70: 748-752.
White, T.C.R. (1971) Lerp insects (Homoptera, Psyllidae) on red gum
(E. camaldulensis) in South Australia. South Aust. Nat. 46: 20-23.
White, T.C.R. (1974) A hypothesis to explain outbreaks of looper
caterpillars, with special reference to populations of Selidosema suavis
in a plantation of Pinus radiata in New Zealand. Oecologia (Berlin) 16:
279-301.
White, T.C.R. (1984) The abundance of invertebrate herbivores in
relation to the availability of nitrogen in stressed food plants.
Oecologia (Berlin) 63: 90-105.
Jeff Shimonski
Director of Horticulture
Parrot Jungle and Gardens
FOOT NOTE: This article was published five years ago. Since
then the use of miticides at Parrot Jungle and Gardens has diminished
even further. This same program of cutting off leaves on the Musoid
plants before they senesce is still in place and still successful.
