Unhealthy Plants Research Articles

Root Feeding by the Beetle Crossidius pulchellus Leconte and Other Insects on Broom Snakeweed ( Gutierrezia Spp.) in Eastern and Central New Mexico 1

Broom snakeweed, Gutierrezia sarothrae (Pers.) Britt. and Rusby, and the closely related threadleaf snakeweed, G. microcephala (DC.) A. Gray were sampled for root-feeding insects at 18 sites in Lea Country and two sites in Lincoln County, New Mexico, in 1978 and at ten sites (nine sites revisited) in Lea County and one site in Guadalupe County in 1979. Of the 600 plants collected in 1978 nearly 60% of the dead or nearly dead plants (76–100% dead material) above 15.2 cm in height contained root borer holes. Less that 15% of the plants 15.2 cm or less in height, whatever their health classification, contained borer holes. Root borer holes were thus most closely correlated with taller, older, unhealthy plants. The longhorned beetle Crossidius pulchellus LeCont appeared to be the major root borer in these populations. Most of the plants collected in 1979 were healthy seedlings and much less borer activity was seen.

The possible role of pathogenic fungi in die-back of Spartina townsendii agg.

A recession of Spartina townsendii, known as die-back, in mud flats in the Hampshire basin, showed symptoms inconsistent with attack by a primary pathogen. Soft-rotted rhizomes of die-back plants contained no bacteria or fungi until rotting was well advanced, and an examination of moribund material revealed no obviously pathogenic fungi. Seedlings planted in sand culture alongside heavily fungus-infected plants grew strongly, and unhealthy plants set beside healthy plants in the field did not pass on the infection to the healthy ones, but themselves recovered. On the other hand, healthy plants transplanted to die-back sites died. It was concluded that attack by a strong primary pathogen was not involved, and that the cause of the disease was essentially non-parasitic. The association of the die-back with certain definite types of site emphasized the need for an investigation of the ecological conditions governing occurrence of the disease.

MAJOR AND MINOR ELEMENT STATUS OF HEALTHY AND UNHEALTHY ALFALFA

A study was made of the major and minor element status of healthy and unhealthy alfalfa. Elements determined were calcium, magnesium, potassium, phosphorus, molybdenum, manganese, zinc and boron. Unhealthy alfalfa was found to be deficient in potassium and/or boron, the critical levels being 1 per cent and 20 parts per million respectively.The levels of other major and minor elements were similar in both healthy and unhealthy plants. Available soil boron was apparently positively correlated with plant tissue boron.

A physiological study of boron deficiency in plants

does not appear. First page follows. Introduction Problems relating to the nutrition of plants have assumed an increasing importance since it is now evident that the so-called micronutrients play an important role not only in the physiology of the plants but often of animals which feed upon them. True, most soils contain these elements, but soils are known in which the amounts necessary for healthy plant growth fall below the critical level. It is a matter of record that the systems of farming in California which expanded horticulture in the latter part of the nineteenth and early twentieth centuries were for a time highly successful, but eventually in certain districts the fruit and vegetable crops were affected with hitherto unknown maladies unrelated to attacks of plant-disease organisms or of insects. The new maladies were termed “dieback,” “yellow leaf,” “sour sap,” “little-leaf,” “mottle-leaf,” “cork spot,” “decline,” and others, all of which connoted a general lack of vitality and fruitfulness. In an attempt to remedy the condition, soil amendments which included a wide range of materials were applied to orchards and fields, sometimes with success, but often contrariwise. When conventional methods of treatment failed to ameliorate the situation, it became apparent that new studies must be undertaken to ascertain the underlying causes of the unexplained crop failures. The problems were investigated from various angles; often false starts were made, but eventually it was discovered that small amounts of the micronutrients could overcome the unthrifty condition of some of the trees. An extensive series of experiments has demonstrated that the application of small quantities of manganese, or iron, or boron, or zinc can often restore unhealthy plants to vigor. Usually the salts of these elements are applied directly to the tree, but in vegetable growing they are applied to the soil.

PLANT NUTRIENTS AND PINE GROWTH

SUMMARY In common with pine plantations established in different parts of the Australian Continent, certain sections of those planted by the Forests Department of Western Australia in the South-West of that State have developed “sick areas,” in connection with which plant pathologists and entomologists have failed to associate any causative organisms. Attention has been given to the possibility of the primary causes of such unsatisfactory growth being attributable to soils being deficient in one or more plant nutrients essential to the growth of the pine crop, and the results of a large number of investigations and experiments along these lines are given. Various unhealthy conditions of P. radiata and P. pinaster are described and attention is drawn to the desirability of standardising names for these conditions. A relation has been established between soil types and pine growth. Chemical analyses have shown that the soils of the majority of plantation sites available are low in plant nutrients according to recognised agricultural standards. The stunting of pines in new nurseries has been overcome by applying a dressing of soil taken from old pines or alternatively spreading fruiting bodies of Rhizopogon luteolus on the area to be used as a nursery. Ash analyses have been made of wood, bark and needles from healthy and unhealthy plants. For some unexplained reason, the figures for Soda (Na2O) were the only ones appearing to have any significance. A study of the nitrogen cycle of soils from virgin eucalypt forest, ploughed land, and plantations showing good and poor growth gave no significant differences. In common with agriculture, remarkable results have been obtained with superphosphate, but Calcium, Nitrogen and Potash have not increased the responses obtained with water-soluble phosphate. Among the experiments carried out to try and ascertain the cause of “rosetting” in young pines was an experiment consisting of spraying the small pines with chemically pure solutions of eight minor elements. Immediate and striking response occurred in colour, length of needle and restoration of normal growth on pines sprayed with Zinc chloride. A parallel series of experiments involving pouring quantities of the same solutions around the roots of the young pines has not given equally rapid and striking results. Other factors discussed are soil changes arising from pasture development prior to planting; cultivation of the planting site; the effect of clearing methods adopted; and the varying reactions to site of different species of pine.