Pecan Leaf Research Articles

Application of Reduced Rates of Systemic Insecticides for Control of Foliar Pecan Arthropods

Placement of aldicarb near the emitters of a drip irrigation system in a mature pecan, Carya illinoensis Koch, orchard in a single application during the spring was an effective control tactic against certain foliar insects. Reduced rates of ⅛, ¼, and ½h of the full dosage (9 kg [AI]/ha) were tested and compared to conventional application of the granules in swathes between trees at the full dosage. The ¼ and ½ reduced doses controlled the pecan aphid complex better than, or equally as well as, full dosage with conventional application. Only the full dose applied near the emitters controlled pecan leaf scorch mites, Eotetranychus hicoriae (McGregor). In a second experiment, single and double applications of carbofuran , carbosulfan, and aldicarb were tested at three rates applied near the drip emitters. Aldicarb controlled both aphids and mites for the entire season. Carbofuran controlled aphids, but not mites, for the entire season. CarbosuIfan only controlled late-season aphids.

Southern Pecan Leaf Phylloxera (Homoptera: Phylloxeridae): Clonal Resistance and Technique for Evaluation1

Forty-six pecan clones (cultivars or selections) were artificially infested with the southern pecan leaf phylloxera, Phylloxera russellae Stoetzel, to determine resistance. The trees were inoculated by attaching branches from‘Mahan’trees infested with overwintering eggs. Thirty-two clones were resistant, and 14 showed various degrees of susceptibility. Some clones formed small galls from the introduced nymphs but formed normal size galls from a native or indigenous population.

Effects of Nitrogen Fertilizer Level on Development and Populations of the Pecan Leaf Scorch Mite (Acari: Tetranychidae)1

Population development and specific effects of the pecan leaf scorch mite, Eotetranychus hicoriae (McGregor), were studied on pecan seedlings grown under N regimes of 0, 200, or 600 ppm. The largest mite population developed on seedlings with N at 200 ppm (recommended level for good orchard maintenance). The size of this population was attributed to enhanced mite reproduction and not to a shorter life cycle. Generation mortality was 65.3% at 0 ppm, 40.6% at 200 ppm, and 37.8% at 600-ppm N. Compared with that of control seedlings, net photosynthesis (Pn) was less in seedlings with mites at 200-ppm N, but was greater in seedlings with mites at 600-ppm N. Seedlings with mites and provided with 200-ppm N were shorter than seedlings without mites, but in the 600-ppm N test seedlings with mites were taller than seedlings without mites.

Biology of the Pecan Leaf Scorch Mite (Acari: Tetranychidae) 1

Eotetranychus hicoriae (McGregor), pecan leaf scorch mite, overwinter as females in the rough bark area on limbs of pecan trees. Data for the 1979 year showed that overwintering mortality exceeded 70%. In the spring, overwintering females began to oviposit within 7 days after initiation of feeding. In laboratory rearings, eggs did not hatch at 18.3°C, and at 35°C 97% of the individuals died as immatures. It is suggested that these temperatures may limit population growth in the field. In the laboratory, higher mortality with increasing temperatures may be due to increasing mortality of individuals that would develop into males.

Pecan Leaf Scorch Mite Control on Louisiana Pecans, 1982

Abstract The study was conducted on mature 'Stuart' pecan trees at the Louisiana State University Pecan Research and Extension Station, Shreveport, Louisiana. A randomized block design was used consisting of 3 blocks with 1 tree per treatment per block. Applications of foliar applied materials were made on Aug 4 using an FMC 957 speed sprayer delivering approximately 30 gal of material per tree. All trees were sampled on Aug 6. Sampling consisted of counting the number of mites on leaflets 2 and 3 for 10 compound leaves per tree. Data were subjected to analysis of variance.

Impact of Fungicides and Miticides on Predatory and Phytophagous Mites Associated with Pecan Foliage 1

Sulfur, the acaricide cyhexatin (Plictran 50W), and the fungicides benomyl (Benlate 50W) and fentin hydroxide (Duter 50W) were field tested against the pecan leaf scorch mite (PLSM), Eotetranychus hicoriae (McGregor), and other mites found on pecan foliage. All materials were toxic to the tydeid, tenuipalpid, phytoseiid, and eriophyoid mites present. Sulfur and cyhexatin acted rapidly and were the most toxic. Depending on species, benomyl and fentin hydroxide caused 40 to 90% reduction within 14 days. Pesticide effects on PLSM were inconclusive because of large variance associated with the populations. Benomyl and fentin hydroxide treatments resulted in change of relative abundance of phytoseiid species.

Low-Pressure Trunk Injection of Dicrotophos and Solubilized Benomyl for Pest Control on Mature Pecan Trees

Injection of the trunks of mature pecan trees with dicrotophos was an effective method for controlling certain foliar pecan arthropod pests in urban plantings where conventional spray equipment is prohibited. Dicrotophos controlled yellow pecan aphids, Monelliopsis nigropunctata (Granovsky) and Monellia caryella (Fitch), when injected once at 1.9g (AI)/15 cm circumference (circ) of scaffold limb or twice at 0.96 g (AI)/15 cm circ. Dicrotophos controlled black pecan aphid, Tinocallis caryaefoliae (Davis), populations when injected once at 3.8 g (AI)/15cm circ or twice at 0.96 g (AI)/15 cm. Injection of the pecan trees with solubilized benomyl reduced pecan scab damage when injected once at 28 g (AI)/15cm circ or twice at 14g (AI)/15 cm circ. Pecan leaf scorch mite, Eotetranychus hicoriae (McGregor), populations were higher in trees treated with benomyl at 28 g (AI)/15 cm circ than in trees treated twice with benomylat 28g (AI)/15 cm circ plus dicrotophos at 1.9g (AI)/15 cm circ, whereas a single injection of dicrotophos and benomylat these rates did not control pecan leaf scorch mites. No chemical residues of dicrotophos were found in pecan fruits at harvest.

Life Tables and Intrinsic Rates of Increase of the Pecan Leaf Scorch Mite13

Life tables were constructed for the immature stages of the pecan leaf scorch mite (PLSM), Eotetranychus hicoriae (McGregor), at 21.1,26.7, and 32.2, and constant illumination (24:0 LD). Immature mortality varied from 81% at 32.2 to 96% at 21.1°C Life tables also were constructed for the PLSM at two photoperiodic regimes (10:14 and 14:10 LD) at 21.1°C. Immature mortality was 48 and 46% at 10:14 and 14:10 LD, respectively. Intrinsic rates of increase (rm) varied from less than 0.001 at 21.1°C and constant illumination to 0.105 at 32°C and constant illumination. The rm values are ca. 50% of those reported for other tetranychids and result from a rearing technique which caused high immature mortality rates.

Pesticide-Induced Differences in Relative Abundance of Mites on Pecans13

High populations of the pecan leaf scorch mite (PLSM), Eotetranychus hicoriae (McGregor), developed on pecan trees sprayed with phosmet but not on trees sprayed with dialifor or a combination spray of phosmet plus carbophenothion. Comparison of trees with a history of yearly pesticide sprays with trees not sprayed for a number of years revealed major differences in relative abundance of PLSM and mites of the families Eriophyidae, Tydeidae, and Phytoseiidae.

Mite Control on Louisiana Pecans, 1979

Abstract Two similar but independent experiments were conducted to control pecan leaf scorch mites on mature “Stuart”, “Schley”, and “Success” pecan trees at Monroe, LA. The experimental design for Experiment #I was a randomized block design consisting of 4 blocks with 2 trees per treatment per block. Applications were made Aug 14 with a Myers 2A42 sprayer with ca. 500 gal being applied per acre. Evaluation occurred on Aug 21 (7 days post-treatment) and Aug 28 (14 days post-treatment) by counting the number of mites present on 2 leaflets on each of 10 randomly selected compound leaves per tree. Data were subjected to analysis of variance.

Development of a Sampling Technique for the Pecan Leaf Scorch Mite 1 and Phytoseiids on Pecan

Studies were conducted for 2 yr in Louisiana to develop a sampling technique for the pecan leaf scorch mite, Eotetranychus hicoriae (McGregor), and associated phytoseiids. Results indicated that tree to tree and leaf to leaf variation in pecan leaf scorch mite, pecan leaf scorch mite egg, and phytoseiid populations was slight regardless of the sample date in the growing season. The greatest variation occurred among leaflets on individual compound leaves; however, the data indicated positive correlations between populations encountered on certain leaflets and combinations of selected leaflets and populations encountered on entire compound leaves. The consequence of these findings should be important for pest management programs currently being developed for pecans. Sampling pecan leaf scorch mites and phytoseiids from paired leaflets would be ca. 10 times faster than sampling in the manner previously described in the literature. The reduction in sampling time would enable monitoring of additional orchards.

Influence of Temperature and Photoperiod on Development and Oviposition of the Pecan Leaf Scorch Mite, Eotetranychus hicoriae1, 3

The life cycle of the pecan leaf scorch mite (PLSM), Eotetranychus hicoriae (McGregor), was studied at 15.5°, 21.1°, 26.7°, and 32.2°C and 30-50% RH on pecan leaf discs. Initial studies at constant illumination (24:0 LD) demonstrated a negative correlation between developmental time and temperature. No eggs hatched at 15.5°C. At a photoperiod of 10:14 and 21.1°C, females exhibited diapause morphology and did not oviposit. Shortening of the photophase resulted in an increase in developmental time for both sexes. Oviposition studies on pecan seedlings at the above temperature regimes showed maximum daily oviposition occurred at 26.7°C. There was no significant difference between oviposition on seedlings and leaf discs. No significant difference was found in the total eggs deposited by mated vs. virgin females. The presence of a tritonymph stage was not confirmed.

Pecan, Yellow Pecan Aphid and Leaf Scorch Mite Control, 1978

Abstract The experiment was conducted at Cleveland, MS. Four rates of Temik and an untreated check were tested in single-tree plots each replicated four times. Application was made on Jun 14 with an Easy-Flow applicator; then the insecticide was incorporated lightly with a drag harrow. The four rates were applied on the basis of tree-trunk-per-inch-diameter. On several dates after application, the mites and aphids present on 20 leaflets and 50 leaflets per plot, respectively, were counted.

Pecan, Yellow Pecan Aphid and Leaf Scorch Mite Control, 1977

Abstract The experiment was conducted at Shaw, Mississippi. The experiment was a completely random design with single-tree plots replicated 10 times. Application of the test materials was made on Aug 15 with a John Bean 757 sprayer calibrated to deliver 12 gal spray per tree. Evaluation was made on Aug 23 and 29 by counting the aphids present on 30 randomly selected leaflets per tree.

Dosage-Mortality Data on the Pecan Leaf Scorch Mite1

Laboratory experiments utilizing the slide-dip technique were conducted to establish base-line dosage-mortality data on Eotetranychus hicoriae (McGregor). The effectiveness of 11 insecticides currently registered for pecans from most to least toxic based on LD50 values were demeton, dicofol, dialifor, azinphosmethyl, disulfoton, phosalone, parathion, methidathion, dimethoate, carbaryl, and endosulfan while the rank of 10 compounds presently not labeled for use on pecans was oxydemetonmethyl, methiocarb, Plictran®, chlordimeform, dicrotophos, monocrotophos, malonoben, Vendex® (hexakis (beta, beta-dimethyl-phenethyl) distannoxane), methomyl, and methyl parathion.

Influence of Spray Programs on Seasonal Abundance of Pecan Leaf Scorch Mite and Phytoseiids in Louisiana1

The population dynamics of Eotetranychus hicoriae (McGregor) were studied from May to Oct. in 3 managed and one abandoned pecan orchard in northern Louisiana during 1975 and 1976. The seasonal abundance of the pecan leaf scorch mite (PLSM) varied in each managed orchard primarily as a result of the insecticide programs followed. In the abandoned orchard, the PLSM exhibited low populations through midseason and eventually reached peak levels in late Aug. Insecticides were shown to be detrimental to the phytoseiid populations and appear to be partially responsible for the larger PLSM populations found in the managed orchards.

Pecan leaf analysis: II. Linear correlation with sampling date over a 5‐year period

Abstract Linear correlations between pecan leaf element concn for 13 elements and 37 different sampling date pairs were determined to study the closeness of the relationship of leaf element conen across dates and years. Correlations were highly significant for leaf Mg, Zn, Mn, and Ba; only fair for Ca, Fe, B, Al, and Sr; and poor for N, P, K, and Cu. Data indicated that the period of the first week of July through the first week of August was about as good as any other period for sampling for all elements.

Pecan leaf analysis: I. Varietal, fertilizer, and seasonal effects

Abstract Differences in elemental content of pecan [Carya illinoensis (Wang.) K. Koch] leaves among cultivars were found for N, P, K, Ca, Mg, Mn and Zn. Of the 7 elements studied, only leaf K indicated a date by cultivar interaction. Differences in leaf K among cultivars became greater as the season progressed. Increasing rate of application of N‐P‐K fertilizer increased leaf N, Ca, Mn, and Al, but had very little or erratic effect on leaf P, K, Fe, B, Cu, Zn, and Sr. There were very few consistent significant fertilizer rate by date interactions for the 13 elements tested. Seasonal trends for element leaf contents from mid‐May through October were generally downward for N, upward for Ca, Mn, Fe, B, Cu, Al, and Ba and changed very little for Mg, Zn, and Sr. Leaf P and K responses to sampling date varied with year. Large year to year variations in leaf trends over dates suggests difficulty in selecting a period for leaf sampling where little change in leaf levels consistently occurs.

Infestation Levels of Pecan Leaf Phylloxera, Phylloxera notabilis Pergande, 1 on Pecan Cultivars 2

Studies conducted for 3 yr demonstrated that significant differences in pecan leaf phylloxera, Phylloxera notabilis Pergande, infestations occurred among 3 cultivars of pecans grown in an orchard that had not been subjected to any insect control practices for over 20 years. Observations during the studies revealed that 8 other cultivars in the same orchard remained virtually uninfested. Sampling data obtained indicated that the distribution of phylloxera galls around a tree was random; however, the density of galls was greater in the lower portions of the trees.

Feeding of Japanese Beetles1 on Phylloxera Galls2

When the pecan leaf Phylloxera, Phylloxera notabilis Pergande, feeds on new spring hickory or pecan growth, a 3- to 16-mm-diam gall forms on leaves (Whitehead and Eastep 1937). The Phylloxeran (stem mother) matures within the gall and lays eggs that hatch in ca. 2 days. When the galls split in ca. 4–5 weeks the offspring escape. This type of attack causes the leaves to become malformed and weakened, and the hickory or pecan growth may defoliate prematurely.