More effort needed to protect crops against PCN

Potato growers are unlikely to halt the spread of potato cyst nematodes until there are commercially appealing varieties with good resistance and tolerance to both species of the pest, Globodera pallida and G. rostochiensis.  

Resistant varieties are considered as the best means of bringing populations down to sustainable levels, but the difficulties in developing varieties that also have strong commercial appeal means such cultivars remain a distant prospect.

Speaking at the Bayer potato conference, Dr Matthew Back, a reader in plant nematology at Harper Adams University, acknowledged that the commercial focus on Maris Piper made PCN control difficult, but encouraged growers to adopt practices across the rotation to better manage the situation.

“There is too much reliance on Maris Piper. Eurostar is the only variety with resistance to both G. pallida and G. rostochiensis available and it accounted for just 0.7% of the planted area in 2021. Until growers have a wider choice of resistant and tolerant varieties, more effort needs to be directed at other measures if land is to be protected,” said Dr Back.   

Breeders recognise the urgency and the commercial opportunity it presents, but aside from a few varieties in trial, there has been few positive developments.

“We need a variety with better characteristics than Maris Piper that also has good resistance and tolerance to G. pallida and, preferably, G. rostochiensis for real progress to be made,” he said.

Cultural measures

With such breeding progress still seemingly a long way off, more novel forms of intervention will be required. Dr Back promotes the viability of cultural controls such as trap and biofumigant crops as well as chitinous soil amendments.

“Biofumigation using crops which contain high in hydrolysed glucosinolates release a form of volatile isothiocyanates, a form of mustard gas. Indian mustard (Brassica juncea) has proven to be amongst those effective against PCN, but success is variable,” said Dr Back.

Solanaceous trap crops, such as sticky nightshade (Solanum sisymbrifolium) and African nightshade (S. scabrum), have been effective reducers of multiplication, up to 70%, but as with Indian mustard, the growing conditions and nutrient availability are key to success.

Another means of PCN control under investigation is the use of chitin. The polysaccharide compounds are found in the shells of crustaceans and can be incorporated as a soil amendment. Chitin increases the proliferation of chitogenic bacteria which act as potential biological control agents.

Chitin is found in the outer cyst shells of nematodes. Chitogenic bacteria proliferate in the presence of a rich source of food, including on the cysts of PCN thereby helping to reduce the number of viable cysts in the soil profile.

The use of Chitin as a non-chemical approach to decreasing PCN infestations isn’t new, but as Dr Back states, “more work is needed to identify the most effective form of chitinous soil amendment”.

While Globodera species are the principal focus of grower efforts to manage plant parasitic nematodes, there are other species of concern.

“The stubby root nematode is the principal vector of tobacco rattle virus, the causal factor of spraing symptoms, so should also feature in soil pest management plans alongside PCN. The root knot nematode (Meloidogyne fallax) has also recently been detected in horticultural activities and, if it were to spread to commercial potato land, this could pose a serious threat to the crop,” said Dr Back.

 Nematicides are part of IPM

Cultural controls and good land stewardship are core to IPM but they are not alone sufficient to protect yields from the threat posed by PCN or free-living nematodes. Velum Prime, the liquid nematicide containing fluopyram with no restrictive harvest interval, is also central to an integrated approach.

Across 43 UK trials performed between 2012 and 2021, the average yield protection afforded by Velum Prime (fluopyram) is 3.7 t/ha over the untreated.

Source: Bayer, 2012-21. Varieties involved include: Maris Piper (13 trials), Maris Peer (11), Estima (3), Markies (3), Arsenal (2), Eurostar (2), Saxon (2), Charlotte (1), Desiree (1), Lady Claire (1), Performer (1), Melody (1), Russet Burbank (1), Innovator (1).

Applied as a standalone treatment, Velum Prime delivers an average yield protection across 43 trials of 3.7 t/ha over the untreated. In higher pressure situations, the yield protection is greater when applied in sequence with fosthiazate.

Since its introduction ahead of the 2019 season, Bayer has strived to be clear about both the contribution that Velum Prime makes to yield protection and the importance of application best practice in making the most of its potential.

“The in-furrow and broadcast-spray-before-incorporation methods deliver similar PCN population management performance and we see that it is effective on its own in low PCN population scenarios. Where PCN pressure is higher, Velum Prime in sequence with half-rate Nemathorin has been shown to deliver more yield protection than full-rate Nemathorin alone,” Richard Phillips, Bayer roots and horticulture campaign manager, observes.

“Importantly, we see that populations as measured using the Pf:Pi ratio show the greatest reduction where Velum Prime is used in sequence with Nemathorin,” he says.