Recent research conducted by Alison Popay and Joanne Jensen of AgResearch, Ruakura, illustrates that new EXTREME™ perennial ryegrass with AR6 endophyte, has excellent resistance to Black Beetle adults.

Black Beetle is a major pasture pest throughout the northern half of the North Island, where mean air temperature is above 13^oC. Adult Black Beetles feed at the base of tillers in a variety of grass species, causing severe damage to plants, in particular younger seedlings. Control and prevention of Black Beetle to date has been by seed treatment (for seedling protection only) or use of wild-type endophyte infected perennial ryegrasses, which cause ryegrass staggers.

AR6 is a non-staggering (no lolitrem B) endophyte that provides resistance to Black Beetle by producing moderate levels of ergovaline. In EXTREME™, ergovaline concentrations are greatest in the crown of the plant (where Black Beetles feed), and relatively low in the leaves, where animals usually graze¹.

Conducted at AgResearch’s Ruakura Research Centre in Hamilton, the trial sown on 22 April, 2003, compared Black Beetle feeding on six seedling and two mature perennial-ryegrass / endophyte combinations. Three weeks after sowing, adult Black Beetles were introduced to each of the ryegrass / endophyte combinations. The number of damaged seedlings was assessed weekly between 4 & 7 weeks after planting and again at 10 weeks, with a final assessment in mid-October. 

The percentage of seedlings damaged by adult Black Beetles was lowest in AR6 EXTREME™, followed by cultivars containing wild-type endophyte, then AR1 endophyte, with the highest level of damage on ryegrass without endophyte. Similarly, in mature plants the percentage of tillers damaged by adult Black Beetles in the wild-type cultivar was significantly lower than the AR1 cultivar (Refer Table 1).

Table 1. Percentage of seedlings damaged by adult Black Beetle in October, 2003.
 

EXTREME™ gave significantly greater protection against adult Black Beetle feeding than AR1 treatments.

These findings support earlier work (Popay & Baltus, 2001)³, which showed that seedling ryegrass infected with AR1 is as susceptible to adult Black Beetle feeding as endophyte-free ryegrass. Popay and Baltus also found that adult AR1 plants were not as susceptible as AR1 seedlings (though they were more susceptible than ryegrass containing wild type endophyte). Results from this current trial (table 1) also confirm that the level of protection provided by AR1 in mature plants was significantly lower than similar plants containing wild type endophyte. 

While these results apply to adult black beetle damage, previous findings by King (1978)² showed that an adequate diet, particularly in spring, is important for egg laying by the Black Beetle. As a result, cultivars such as EXTREME™ with AR6, which greatly reduce the feeding by adult Black Beetle, are expected to be exposed to lower levels of egg laying, and therefore lower numbers of the damaging black beetle larvae. This is because the beetle may either disperse to find other food sources, or reduce feeding to such an extent that both their winter survival and reproductive capacity is severely compromised.

Based on the results of this trial, AR6 EXTREME™ is expected to show robust resistance to Black Beetle in the field.

¹Ergovaline levels are highest in the crown of the plant during summer and autumn.  Ingestion of ergovaline can affect animal performance and health. To minimise any adverse effects, avoid prolonged set stocking, or grazing of fresh regrowth, of such pastures during summer and autumn. Set stocking can occur during winter and spring, but for best pasture production, persistence, quality and best animal condition and performance, research indicates that farmers should practice rotational grazing. If in doubt, always seek professional advice.

² King, P.D. (1978). The effect of diet on fat levels and fecundity of Heteronychus arator (Coleoptera: Scarabaeidae). Proceedings of the 2^nd Australasian Conference on Grasslands Invertebrate Ecology. Palmerston North, New Zealand 22-26 May 1978, pp.97-99.

³  Popay, A.J. and Baltus. J.G. (2001). Black beetle damage to perennial ryegrass infected with AR1 endophyte. Proceedings of the New Zealand Grassland Association 63: 267-271