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Effect of integrating soil solarization and organic mulching on the soil surface insect community.

Mulching by spreading organic matter around plants is an effective

method to manage some pest insects as well as weeds (Brown &

Tworkoski 2004; Johnson et al. 2004). Mulches provide shelter for

predatory insects (Pullaro et al. 2006). Soil solarization, a

hydrothermal method of managing nematodes, diseases, insects, and weeds,

is accomplished by passive heating of moist soil covered with

transparent plastic sheeting (McGovern & McSorley 1997). Because of

the lethal effects from high soil temperature, solarization must be

conducted before crops are planted. The objective of the present study

was to evaluate the integrated effects of solarization and organic mulch

on the soil surface insect community, including non-target and

beneficial insects.

Field experiments were conducted in fall 2008 at the University of

Florida Plant Science Research and Education Unit (lat.

29[degrees]24’N, long. 82[degrees]9W), near Citra, FL. The soil was

Arredondo sand (95% sand, 2% silt, 3% clay) with 1.5% organic matter.

The field was rototilled in Jul, and beds were formed (20 cm high, 76 cm

wide, with 1.8 m between bed centers). Individual plots were single

beds, 9.14 m in length. Average soil moisture measured gravimetrically

before bed formation was 8.7%.

Four treatments were arranged in a randomized complete block design

with 5 replications. The treatments compared were: solarization (S) =

plastic pre-plant, nothing post-plant; mulch (M) = mulch pre-plant,

mulch post-plant; mulch + solar (MS) = plastic pre-plant, mulch

post-plant; and control (C) = nothing pre-plant, mulch post-plant. For

the mulch treatment, a pre-plant mulch of sunn hemp (Crotalaria juncea

L.), 3 cm thick (8.16 kg total weight/plot), was applied over the bed

surface on Aug 13. In the solarization treatment, beds were covered with

Polydak[R] (1.3-milthick, UV- stabilized, transparent film, Ginegar

Plastics Products, Ginegar, Israel) plastic film for 6 weeks beginning

on Aug 12 as described by Gill et al. (2009). After 6 weeks, plastic was

removed, and all beds were planted with ‘Potomac Pink’

snapdragons (Antirrhinum majus L.). Mulch was again applied on Oct 2, as

a main mulch application, to M, C, and MS treatments. Note that is not

possible to have mulch and solarization plastic present on a plot at the

same time.

Soil surface insects were sampled with plastic sandwich containers

(14 cm x 14 cm x 4 cm deep) used as pitfall traps as described by Borror

et al. (1989). Each pitfall trap was placed in the center of the plot

and buried so that the upper edge was flush with the soil surface. Traps

were filled three-quarters full with tap water, and 3 to 4 drops of dish

detergent (Ultra Joy[R], Procter & Gamble, Cincinnati, OH) added to

break surface tension, and ensure that the insects remain in the trap.

Traps were set out in the morning and collected before noon the next day

(recorded as the sampling date). Traps were placed in cold storage

(10[degrees]C), contents transferred and stored in 70% ethanol, and

insects were identified to order and family and counted.

Data were subjected to one-way analysis of variance (ANOVA) with

the Statistical Analysis System (version 9.1; SAS Institute, Cary, NC).

Treatment means were separated based on the least significant difference

(LSD) range test, at P [less than or equal to] 0.05.

Preplant mulching or solarization was useful in reducing weeds in

the plots. The main weeds were nutsedges (Cyperus spp.), grasses,

Florida pusley (Richardia scabra L.), purslane (Portulaca oleracea L.),

and hairy indigo (Indigofera hirsuta L.). The percentage of the plot

surface area occupied by weeds averaged 3 to 5% in MS, ca 90% in C, 20

to 25% in S, and 35 to 40% in M plots, respectively.

On most sampling dates, Collembola populations were higher in the M

treatment than in the S treatment (Table 1). Collembola are associated

with decomposing organic matter (Colemen & Crossley 1996), which was

provided by sunn hemp in the M treatment. Collembola were not as

abundant in S plots, possibly because mulch was absent. In addition, the

solarization process itself may have reduced populations that were

present in soil.

Many groups of arthropods, including spiders, ants, grasshoppers,

crickets, elaterids, and staphylinids were unaffected by the treatments

(data not shown), but interesting trends were observed in some others.

Cicadellids were more abundant (P [less than or equal to] 0.10) in C

plots (12.0 [+ or -] 2.59/ trap) than in MS plots (5.8 [+ or -]

2.42/trap) on Nov 9. On Oct 28, highest numbers (P < 0.10) of

carabids (0.8 [+ or -] 0.37/ trap) and flea beetles (0.4 [+ or -]

0.24/trap) were observed in S plots. Highest numbers (P < 0.10) of

dolichopodids (8.0 [+ or -] 2.43/trap) were observed in S plots on Dec

8. Solarized plots were free of mulch and had relatively low weed

levels, both of which might influence insect movement. Environmental

heterogeneity is known to interfere with movement and host finding of

flea beetles and other insects (Root 1973; Smith & McSor ley 2000).

On Oct 28 and Nov 9, other plant feeders (whiteflies, thrips, and

aphids) were significantly higher (P < 0.05) in the C treatment

compared with the other 3 treatments (Table 1). It is possible that

whiteflies, thrips, aphids, and maybe leafhoppers were present and fed

on the abundant weeds in the control treatment. Treatments that limit

weeds may be helpful in limiting these plant-feeding insects as well.

Integrating solarization and mulching did not have much overall impact

on the insect community, compared to solarization alone, but it did lead

to recovery of Collembola populations later in the season to similar

levels found in mulched plots.

SUMMARY

Integration of solarization and organic mulch did not affect the

insect community as much as solarization alone. Solarization and

mulching influenced Collembola population levels and occasionally

affected other insect groups, depending on their behavior. Plots without

solarization or mulching developed heavy weed levels and increased

levels of plant-feeding insects.

REFERENCES CITED

BORROR, D. J., TRIPLEHORN, C. A., and JOHNSON, N. F. 1989. An

Introduction to the Study of Insects, pp. 751-753. 6th ed., Saunders

College Publishing, Chicago, IL.

BROWN, M. W., and TWORKOSKI, T. 2004. Pest management benefits of

compost mulch in apple orchards. Agric., Ecosyst. Environ. 103: 465-472.

COLEMAN, D. C., and CROSSLEY, JR., D. A. 1996. Secondary

production: Activities of heterotrophic organisms–the soil fauna, pp.

51-106 In Fundamentals of Soil Ecology. Academic Press, San Diego, CA.

GILL H. K., MCSORLEY, R., and TREADWELL, D. D. 2009. Comparative

performance of different plastic films for soil solarization and weed

suppression. Hort Tech. 19: 769-774.

JOHNSON, J. M., HOUGH-GOLDSTEIN, J. A., and VANGESSEL, M. J. 2004.

Effects of straw mulch on pest insects, predators, and weeds in

watermelons and potatoes. Environ. Entomol. 33: 1632-1643.

MCGOVERN, R. J., and MCSORLEY, R. 1997. Physical methods of soil

sterilization for disease management including soil solarization, pp.

283-313 In N. A. Rechcigl and J. E. Rechcigl [eds.], Environmentally

Safe Approaches to Crop Disease Control. CRC, Lewis Publishers, Boca

Raton, FL.

PULLARO, T. C., MARINO, P. C., JACKSON, D. M., HARRISON, H. F., and

KEINATH, A. P. 2006. Effects of killed cover crop mulch on weeds, weed

seed, and herbivores. Agric., Ecosyst. Environ. 115: 97-104.

ROOT, R. 1973. Organization of a plant-arthropod association in

simple and diverse habitats. The fauna of collards (Brassica oleracea).

Ecol. Monogr. 34: 95-124.

SMITH, H. A., and MCSORLEY, R. 2000. Intercropping and pest

management: A review of major concepts. American Entomol. 46: 154-161.

HARSIMRAN K. GILL and ROBERT MCSORLEY

Entomology and Nematology Department, University of Florida,

Gainesville, FL 32611-20

Table 1. Effect of treatments on insect taxa (numbers/pitfall

trap) on selected sampling

dates–2008.

Other plant

Treatment (1) Collembola feeders (2)

Oct 13

MS 10.2 b [+ or -] 3.34 1.6 a [+ or -] 0.51

C 21.8 ab [+ or -] 5.46 4.4 a [+ or -] 1.54

S 14.6 b [+ or -] 5.33 3.8 a [+ or -] 0.97

M 32.2 a [+ or -] 6.63 6.8 a [+ or -] 3.34

ANOVA (3)

F value 3.26 1.24

P value 0.0492 0.3268

Oct 28

MS 13.8 b [+ or -] 4.93 1.0 b [+ or -] 0.45

C 15.0 b [+ or -] 1.76 7.6 a [+ or -] 2.87

S 12.0 b [+ or -] 1.52 2.4 b [+ or -] 1.03

M 32.8 a [+ or -] 3.51 0.6 b [+ or -] 0.40

ANOVA

F value 8.9 4.3

P value 0.0011 0.0209

Nov 9

MS 46.6 a [+ or -] 8.25 0.8 b [+ or -] 0.37

C 34.4 b [+ or -] 6.45 6.4 a [+ or -] 2.38

S 14.0 b [+ or -] 3.73 1.6 b [+ or -] 0.81

M 32.6 a [+ or -] 5.35 1.6 b [+ or -] 0.51

ANOVA

F value 4.76 3.9

P value 0.0148 0.0287

Dec 8

MS 21.8 ab (4) [+ or -] 3.80 3.0 a [+ or -] 0.71

C 34.4 a [+ or -] 7.56 1.6 a [+ or -] 0.93

S 16.0 b [+ or -] 2.61 2.6 a [+ or -] 0.75

M 24.2 ab [+ or -] 2.24 2.0 a [+ or -] 0.84

ANOVA

F value 2.83 0.59

P value 0.0717 0.6302

(1) Solarization (S) = plastic pre-plant, nothing post- plant;

mulch (M) = mulch pre-plant, mulch post-plant; mulch + solar

(MS) = plastic pre-plant, mulch post-plant; and control (C) =

nothing pre-plant, mulch post-plant.

(2) Other plant feeders include whiteflies, aphids, and thrips.

3Statistics from analysis of variance (ANOVA).

Data are means [+ or -] standard error of 5 replications. Means

followed by the same letters do not differ significantly based on

LSD test (P [less than or equal to] 0.05)

(4) Mean separation at P [less than or equal to] 0.10

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