IPM in Hydroponic Strawberries

We caught up with long-time friend and colleague Neil Helyer at a recent IOBC conference on greenhouse IPM R&D developments in the south of England. We reported on the conference in the previous issue of PH&G. These conferences, held every 3 years, always have farm visits, which are opportunities to see how EU and UK greenhouse hydroponic growers are progressing with their IPM programs. This year was no exception, with successful IPM on display in a range of different crops.

We were particularly impressed with the IPM program in hydroponic strawberries at Donaldsons Nursery at Chichester and spoke to Neil at length about it. Neil is an IPM consultant with the Fargro Green Team and advises Donaldsons on pest and disease matters. Fargro is a horticultural supply company based at nearby Littlehampton. Having access to a competent consultant is a good idea for IPM as well as for hydroponic crop growing advice and is commonplace in the UK. Good growers use competent consultants all the time, leaving nothing to chance.

Donaldsons Nursery is one of seven farms across southern England within Hall Hunter Partnership (HHP), one of the largest producers of soft fruit in the UK. HHP is a family- owned enterprise (www.hallhunter.co.uk) that originated in 1966. It has a policy of sustainability, producing quality, fresh strawberries (9.5ha glasshouse hydroponic triple-cropped and 180ha field in polytunnels, some double-cropped), raspberries (6.8ha glasshouse and 30.8ha field in polytunnels), blackberries (6.4ha glasshouse in autumn and 12.8ha field in polytunnels), and blueberries (60ha field). That’s a whopping 306ha of soft fruit-producing area, but we will confine ourselves to their glasshouse hydroponic strawberry production at the Donaldsons site.

Within HHP, Donaldsons is the largest production site under cover. Previously an old World War II airfield, it first produced all-year-round chrysanthemums in a 1.3ha glasshouse. In 1987 a further 2.7ha called ‘A Block’ was built, but it is now regarded as old-style Venlo with 2.3m to the gutter. In 2006, 3.7ha of modern style Venlo glasshouse with 9.6m wide bays and 5m to gutter height called ‘B Block’ was added. Collectively, the 6.4ha supplied chrysanthemums to the Sainsbury and Waitrose supermarket chains. However, in 2010, faced with massive energy price increases and low prices, two of the original owners, Colin and Alan Frampton, sold to HHP, who now use the facilities to produce early strawberries hydroponically.

Growing strawberries hydroponically

A previous article (PH&G Issue 121) identified a number of challenges for hydroponic strawberry production, including the need to produce large quantities of fruit per unit area against the challenges of optimising light availability. At HHP Donaldsons, plants are grown hydroponically in coir (cocopeat) for root stability in white plastic pots. Pots are held in rows on a suspended gutter to maximise plant density and to produce high quality strawberry fruit. Suspended gutters provide less under-canopy restrictions and it is easier to remove debris. A standard pipe and rail system is used for picking and spraying. Thermal screens are being installed to save energy when heating early in the season. The older glass in A Block has lower light values. At the time of our visit to B Block, the strawberry crop looked in perfect health, with no visible pest or disease problems and a large crop of fruit coming on.

Strawberry production at this site is still being tweaked, but at the time of our visit, the cropping cycles shown in Table 1 were in place. The first year of triple cropping in B Block in 2011 has been a success and is being refined. Fruit yields are 32% greater in the triple-cropping system under the better glass in B Block, compared with the older glass in A Block.

IPM in hydroponic strawberries

For us though, our particular interest was in hearing about their IPM program managed by the Fargro Green Team. Fargro supplies pesticides and biocontrol agents, amongst other products, plus an IPM service courtesy of Neil and Josh Burnstone. Fargro first became involved with HHP Holland nursery in 2006. Sitting down with Neil it became apparent that there wasn’t much difference between what is encountered at HHP Donaldsons and that in Australia. The key issues, the pests, were the same. The IPM tools also were the same. The recipe for success was simply the management of the various components, and of course crop monitoring. This is the key to success in any IPM program.

However, underpinning this IPM success story is the philosophy of HHP. Across their business, be it field or greenhouse production, HHP is committed to developing systems that ensure they are environmentally and socially acceptable. They aim to leave as light a footprint as possible. The result is healthy food for consumers. Having the absolute support and confidence of the owners has been the key to IPM success at HHP Donaldsons. This is the most important commitment of all. If we can moralise for a bit, a lot of growers talk the talk, but when the chips are down, as we say in Australia, they rush back into the heavy-handed chemical safety net. There is nothing worse or more guaranteed to fail any attempt at IPM than growers who are not 100% committed to IPM and to all facets of its practice. It is a common experience that at some stage when chemical use is reduced, previously unnoticed or minor pests may emerge. This is not a time to panic, but to have confidence in the expert advice provided to you and to be well prepared for such contingencies. It may take a bit of trial and error, but a sound IPM strategy for these new challenges will win out and become just another part of the overall program. Every IPM program should include good hygiene practices. At HHP Donaldsons, between crops they disinfect with Jet 5 (peroxyacetic acid) through the irrigation system and over the whole structure and maintain a clean glasshouse throughout the crop production period.

IPM at HHP Donaldsons

So what was it about the IPM program at HHP Donaldsons that appealed to us? Like all good IPM programs, decision-making at their strawberry site is underpinned by scouting or crop monitoring. Crop walking, as it is called there, is undertaken by DLV Plant UK. They provide an independent crop monitoring and crop protection advisory service. DLV, a Dutch agronomic service, makes monthly visits. The glue that keeps this train on the rails is provided by the local service through Josh and Neil, who visit HHP Donaldsons at 3-4 weekly intervals and also undertake crop walking, mainly in areas previously identified as either being at risk or with known pest and disease concerns. Being local, they can visit at any time at short notice. Neil works closely with HHP’s Daniel van der Veen, who has responsibility for pest and disease matters and IPM programs, crop monitoring and devising pest and disease preventative and curative measures across all HHP sites, including Donaldsons. Daniel travels around all sites on a weekly basis. He is in constant contact with Fargro on the preparation of schedules. Neil estimated that weekly crop walks can add up to several kilometres per day at the large Donaldsons site and is testament to their commitment to IPM.

As the scout walks the crop he taps plants onto a laminated sheet of white squares the size of an A4 page. The lamination not only provides protection from frequent handling, but also stiffens the paper so that it can be held by an edge when tapping foliage, flowers, or shaking fruit over it. Pictures of key pests and biocontrol agents to confirm identifications are available to assist the scout, and to help growers learn to recognise the key pests and beneficials alike. Counts for each block are added up and these are used to modify the proposed schedule if there is a particular problem. Yellow and blue sticky traps are also used at about 1000/ha depending on the risk period as well as acting as mass trapping for control in some instances. Blue sticky traps haven’t really caught on in Australia, with yellow traps the norm. At HHP Donaldsons, traps are changed as necessary, depending on the number of trapped insects on them. Yellow is generally attractive to several winged insect pests, while blue is considered to be particularly attractive to female western flower thrips (WFT), if that level of detail is important to you.

A critical part in designing any IPM program is to identify a list of second line-of-defence chemicals that provide growers and IPM consultants with the means to correct out-of-balance pest populations or to reduce populations of emerging new pests. The chemicals, where possible, should provide a measure of control of up to 50-60%, but it is not necessary for that to be 100%. Different chemical groups will also give choice for resistance management purposes.

Strawberry pestsThe key pest in strawberries causing most economic damage and potentially the most difficult to control is thrips, predominantly WFT. No surprise there. Onion thrips can also be frequently present. Marilyn undertook an intensive study into thrips damage and their threshold levels in strawberries in Australia a few years back. This work was published. Marilyn concluded that damage to young green fruit was more serious than to colouring fruit, so monitoring in flowers was particularly important. An action threshold of 45% of flowers with five or more adult WFT was suggested. Spider mite and aphids are also common at HHP Donaldsons. The main problem with WFT is its resistance to spinosad, a problem experienced in Australian WFT populations also. Neil said that one of the difficulties in using spinsosad is that some growers have been advised to apply it at the time of fast drying. As a translaminar-acting chemical, it should actually remain as a wet residue on the leaf surface for 2-3 hours for best results. A number of chemicals used here act similarly. In the strawberry crop in B Block, the normal sequence of pest occurrence was for aphids to appear first, followed very soon by thrips and later in the season by spider mites. He said that capsid, or mirid bugs as they are more commonly known, can be a problem and caterpillars can occur also. In some seasons though, spider mites can over-winter on the glasshouse structure while the heating is turned off. Once the heating is turned on in late January, the mites awaken and move into the crop where they resume feeding and breeding. In these circumstances, preventive acaricide sprays are applied.

2011 IPM program

In 2011 an early infestation of over-wintered spider mites is exactly what happened in B Block. Key pests, plus the beneficials and second line-of-defence chemicals used in both crops are shown in Table 2.

Chemical use

In the spring crop, the IPM program kicked off with some preventive sprays of etoxazole for motile mite stages and clofentezine for eggs of spider mite, plus abamectin, bifenazate and tebufenpyrad against residual spider mite populations, plus pirimicarb for aphids, in February-March. Fenpyroximate and the biorational chemical SB Plant Invigorator (SBPI) were also used on spider mite. Pymetrozine, pyrethrum and SBPI were used as needed on aphids. Some of the acaricides can be harmful to beneficials, but if they are used early enough and with time for their residues to wear off, then minimum impact is experienced when the biocontrol agents (BCAs) are introduced. Chemicals like etoxazole and abamectin fall into this category. You might think the above program was a bit heavy handed, but the main aim was to reduce the overall pest levels, thus reducing the amount and cost of beneficials that need to be introduced, as you can’t release BCAs into established pest problems. Towards the end of the crop, two sprays each were applied to clean-up residual thrips, aphids and spider mites, so as not to leave a residue of pests that may attack the next crop, which is brought into the glasshouse only a few days after clearing out the old crop and sterilising the house. The pesticides are UK registrations.

Neil said: “Capsids remained outside in 2011 and no damage was recorded in the crops. The main problem with capsid is that damage shows a week or so after the initial feeding by which time many have flown in or out of the house. As a control we have found pymetrozine works well. Pyrethrum is also good as a contact treatment and with short persistence it integrates reasonably well. This is the one pest that can terminate a successful biocontrol program.”

A number of fungicides are used for powdery mildew and Botrytis, respectively (Table 2). As with insecticides, aside from their effectiveness, a choice from different chemical groups minimises the risk of the organisms developing resistance to any one of them.

BCA release program for seasonal pest control

Neil said that in this context, “biocontrol should really be considered as (more) biological maintenance. If a pest problem is present, always use a selective spray to reduce the pest numbers before introducing beneficials to mop up

and maintain pest control. Invariably, there is no spray that is 100% effective. This can be due to a number of factors including the vagaries of leaf structure, density of plant canopy, pest life cycle (many pests insert their eggs or hide them close to leaf veins, pupal stages may be off the plant in the potting media, mites have two resting stages (proto-nymph and deuto-nymph), winged adults can simply fly off to another area and return later). “

He said, “pesticide use before bees and beneficials is fairly normal here (UK), (and that he) uses very similar systems on most other seasonal crops such as nursery stock that tends to be grown cold in older glasshouses or tunnels. A spray of pymetrozine (aphids) plus abamectin (spider mites) 7 to 10 days before starting a beneficial schedule works really well and saves a lot of money.” BCA releases into the spring strawberry crop occurred from early March through to mid-April, mainly relying on two releases of Phytoseiulus persimilis each at 0.5/lin.m, with one also of Amblyseius (Neoseiulus) californicus at 5/lin.m. in loose material for spider mite. For thrips, mainly WFT, two releases each of Amblyseius (Neoseiulus) cucumeris, one in controlled release sachets (CRS) at 1CRS/2 lin.m, and the second release in loose bran plus vermiculite at 250,000 predatory mites/8 rows and Orius laevigatus at 3/lin. m, while for aphids, a number of spot treatments of Aphidius CE mix comprising Aphidius colemani and A. ervi, plus the green lacewing Chysoperla sp. were made. While mainly released for thrips, Orius will also feed on aphids. The CRS technology isn’t yet available in Australia, but James Altmann at Biological Services is working to introduce it as a crop delivery mechanism for Cucumeris in the near future. Each sachet has an active life of 6 to 8 weeks that ensures good predatory mite establishment. Blue sticky traps with WFT lures were positioned through the crop at 1/60 m2. Sometimes traps are increased to 1/10m2, depending on the level of risk and if called upon as a control measure to mass-trap thrips.

Following removal of the spring crop of cv ‘Sonata’ in mid July, an autumn crop of cv ‘Elsanta’ was planted in early August, and an IPM program was commenced in late August. Due to the high mobility of predatory mites, although the old crop was sprayed and removed there were still high numbers of carry-over beneficials, meaning that few new releases were required and even fewer chemical sprays were applied. New releases of BCAs were only needed for thrips and spider mite, while a single spray of the biological insecticide Bacillus thuringiensis was applied for caterpillars late in the crop.

It is common practice for growers to source their BCAs from a single supplier, but in the case of HHP Donaldsons they obtained theirs from Koppert, Syngenta Bioline and BCP Certis. Bumblebee hives for pollination were introduced into the spring crop at 1000 bees/ha in late March, and into the autumn crop at 800 bees/ha in early September. While HHP Donaldsons’ actually preferred honey bees, they proved more difficult to obtain and tended to fly only when favourable weather conditions prevailed. Honey bees are efficient pollinators, but finicky.

This IPM program is a good case study for any grower aspiring to try IPM. Carefully put together using the advice of IPM consultants and regular crop walking, a close eye is kept on pest populations and on the choice of any pesticides used to back-up the beneficials to ensure minimum disturbance and to prepare the crop for the introduction of beneficials. We visited the autumn crop in mid-September during the conference and the plants looked very healthy and productive under this regime. Neil’s good working relationship with Daniel van der Veen ensured that nothing was left to chance. The results spoke for themselves.

About the authors

Stephen Goodwin and Marilyn Steiner are IPM consultants trading as Biocontrol Solutions at Mangrove Mountain.

Acknowledgement

The authors would like to thank Neil Helyer, Fargro Green Team, for providing information for the article.


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