Biological control treatments typically are not as effective as organic chemical treatmentsfor management of crop diseases. Similarly, fertilizers based on phosphorous or siliconhave been demonstrated to suppress but not control diseases. These types of alternativedisease control strategies are much needed by the organic vegetable industry to managedisease and produce quality products�but, reliability of alternative treatments must beimproved. A series of studies were conducted on several vegetable crops in 2002 todetermine if combinations of these strategies would enhance control beyond thoseobserved with individual treatments. The effort was focused on achieving levels of controland yields equivalent to chemical control practices. BioYield with demonstrated ability tocontrol pathogens by antagonism and host induced resistance was paired with silicon andphosphorous acid treatments that suppress disease by several mechanisms. The objectivewas to integrate multiple small-effect strategies to produce levels of plant disease controlequivalent to those achieved with organic pesticides.

Introduction

A root inoculating bacterial preparation (BY, BioYield Concentrate from Gustafson, Inc.(a mixture of Paenobacillus macerans and Bacillus amyloliquefaciens*) was used aloneand in combination with two fertilizer treatments (Calcium silicate (Si)** and pHortress(pH)*** (0-37-25) foliar-applied fertilizer) and a foliage-inhabiting Bacillus cereus (BP-24a). The root inoculating bacteria were incorporated into a peat based media mix (Scott�sRedi-Earth) used for seeding and growing transplants. Similarly, the calcium silicate wasmixed with the media, following which media were seeded into 90ml Cone-tainers.

After 4-6 weeks, broccoli and squash were transplanted into high-tunnel plastic houses inhills or rows as shown in Figs. 1 & 2. Treatments were replicated 6 times in a randomizedcomplete block design, and 3 of the 6 replications were treated with pHortress. BP24a wasapplied at log 7/ml of spray solution at 240-500 L/ha. The pHortress fertilizer wasapplied as a foliar spray at 4L/ha (product) on a 2-week schedule. Similarly, tomato andcucumbers were planted into black mulch-covered, bedded rows and treated withpHortress or BP24a as before.

Tomatoes were evaluated for early blight and bacterial blight severity as the seasonprogressed, while squash were evaluated for anthracnose and powdery mildew. Plantgrowth and disease severities were evaluated at regular intervals during the season, andproduce harvested as the crops matured. All trials received supplemental irrigation tomaintain optimal plant growth. For all trials, the summer of 2002 was hot and dry, anddisease was slow to develop. Due to early onset of winter conditions, squash were notharvested. Data were analyzed using SAS.

ResultsFour to six weeks after seeding, and before transplanting, there were differences in growthamong treatments for all vegetables tested. Enhanced growth was observed in mediaamendments containing root inoculating bacteria, but not for those receiving silicon. Priorto transplanting, there was no visible pathology observed on plants in any treatment.

Typically, growth differences observed in the greenhouse were not observed at significantlevels beyond one month after transplanting. Diseases developed strongly in tomatoes(Figs. 4, 6, & 7) and squash (Fig. 5). Broccoli developed no observable diseases, yetexhibited large yield increases (Fig. 3). A second trial conducted in (2003) on broccoli,provided an 18% yield improvement with BioYield, a 4.5% increase with ZX, and a 11%increase with silicon. Addition of the foliage biocontrol agent BP24 added 11% to BYyields, and 17% to ZX yields. Significant effects on tomato early blight (Alternaria solani,Fig. 7), bacterial wilt (Clavibacter michiganense, Fig. 6) and on yield (Fig. 8), wereobserved on tomatos treated with either BioYield, silicon or pHortress and theircombinations. Strong yield increases of 10-30% were detected on most crops with theuse of BioYield, calcium silicate, or pHortress foliar fertilizer, Additive benefits fromtreatment combinations were most often found where disease was severe.

Footnotes*Applied at ~2kg of BioYield Concentrate per m3 of Scott�s Redi-Earth for all vegetables excepttomato, which was treated with a 4 kg/m3 rate.**Calcium silicate (Calcium Silicate Corp. Lake Harbor, FL) was applied at a rate of 5kg per m3

of media mix.***pHortress flowable foliar fertilizer (Western Farm Service, Fresno, CA) 0-37-25 containing0.2% Mn and Zn.

Figure 2: Butternut squash at earlybloom, and just prior to powderymildew onset. Minor differences inplant growth are still observable.

Figure 4: Mountain Springtomatoes showing effects ofbacterial wilt, as well astreatment differences inducedprimarily by pHortress

Discussion and Conclusions

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Bravo Bravo/pH Alt.

NoneBYSiBY + SiNone + BP2YBY + BP24BY + BP + Si

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9/20 9/23 9/26 9/29 10/2 10/5 10/8

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Disea

se R

ating

(1-5)

No TreatmentsBP24 onlypHortress OnlypHortress +BP24BioYield +BP +pHAgroPro ZX +BP +pH

Results demonstrated two very different responses in treated vegetables. The first was thatyields could be greatly affected with little or no apparent disease (broccoli, Fig. 3). Thiscould have been due to chronic undetected diseases, deleterious rhizobacteria or changes infertility. Squash and tomato both responded with improved disease control. When treatedwith two or more products. For powdery mildew in squash, the effects of pHortress on thislargely external disease were large and additive to effects by root-applied biocontrol agents(BY and ZX) and to the foliage applied biocontrol agent (BP-24a). Similarly, levels ofearly blight and bacterial wilt in tomatoes (Figs. 6 & 7) were both suppressed by individualand combination therapies. Combinations produced highest levels of disease control andhighest yields of tomato fruits (Fig. 8). Research continues on finding appropriatecombination therapies that will maximize both disease control and yield.

Figure 7. Effect of biological control agents andfertilizers used alone and in combinations on severity ofearly blight in tomatoes

Figure 6. Effect of biological control agents andfertilizers used alone and in combinations on severity ofbacterial wilt of tomatoes

Figure 5. Disease progress curves for powdery mildewof squash as affected by biological control agents andfertilizers and their combinations.

4000

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NoneBYSiBy + SiZX

Broccoli Yields kg/ha

Early Blight Severity (1-5)

Bacterial Wilt Severity (# Diseased Plants)

Combining small-effect treatments enhancesnon-chemical disease control and yield of vegetables

BACKMAN, P.A.1, M. Orzolek2, W. Lamont2, C. Dorman1 and N. Conrad1

The Pennsylvania State University, 1Dept. Plant Pathology, and 2Dept. Of Horticulture, University Park, PA 16802

Figure 3. Yield response of broccoli to biocontrolagents and fertilizers in the absence of disease

Methods

Figure 1: Broccoli just prior to harvest with littleapparent disease but providing 20-30 percentyield responses.

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none BY

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Figure 8. Yield Response of Tomato to Biological Control Treatments & Combinations

Treatments

AcknowledgementsThe authors would like to recognize the important contributions of Mr. Mike Miller and theLewisburg Federal Prison and its ICC Camp for providing land and manpower for the vegetabletrials.We also recognize with thanks, the financial support of the Pennsylvania Vegetable GrowersAssociation

Contacts:Paul Backman, Dept. Plant Pathology, 221 Buckhout Laboratory, Penn State University, PAEmail: pbackman@psu.edu, Phone: 814-865-6687