Your choice of mulch dramatically affects plant growth and yield!

 This year we carried out demonstrations on 3 biodegradable mulches and 3 non-biodegradable mulches to see how they compare in a sweet potato production system here in Nova Scotia.

As horrible as this year turned out to be, it was the perfect year to trial plastic mulches as for many they made the difference between growing a marketable crop.. or not. Sweet potatoes are a challenging crop to grow in N.S, they need a long season with warm soils to produce tubers that make grade.

We demonstrated six different mulches, 3 biodegradable, and 3 nondegradable to test a variety of colours and thicknesses/material. There was a 30% difference in yields between the highest and lowest performers as well as differences in tuber grades (sizing) for each mulch. Before I talk about the treatments, it’s important to remember that this is not a replicated trial; the results highlight striking differences between mulches, but this is by no means conclusive.

Treatments:

-          Dubois, black, 1 mil embossed plastic (non-degradable)

-          Heartnut Grove, green, 1 mil (non-degradable)

-          Solar Shrink, black, 0.5 mil (non-degradable)

-          Film Organic “88”, black, 0.8 mil (biodegradable)

-          Dubois Bio360, black, 0.5 mil (biodegradable)

-          Dubois Bio360, clear, 0.5 mil (biodegradable)

Method:

-          3 rows, 400ft long, of each of each mulch was laid on June 13, 2023. Raised beds were 10" high, 28" wide.

-          Slips planted in late June. Management practices identical to rest of field (fertility, pesticides, etc)

-          12ft sections from each row were harvested Sept 19. Weighed for above and below ground biomass; tubers graded with a standard sizing board (<1.5”; 1.5” – 2.0”; 2.0” – 3.5”; >3.5”).

Results:

The table 1 below details specific results, with green highlighting showing the best performer in each category/column. Here are some brief takeaways:

-          The three non-degradable mulches produced the highest grade A (2” – 3.5”) tubers.

-          The green mulch produced the highest average weight per tuber (160 g) and stimulated root growth over shoot growth (root to shoot ratio).

-          The two Dubois biodegradable mulches were slightly too thin. The black 0.5 mil adequately controlled weeds but was severely degraded by September. The clear 0.5 mil had ruptured by July 20^th and was overrun by weeds.

-          From these results I would recommend choosing a black biodegradable mulch no thinner than 0.6 mil and a clear biodegradable mulch no thinner than 0.8 mil.

-          We did not assess the cost difference between each mulch or consider the added cost of removing nondegradable mulches at the end of the season. These costs needed to be factored in to determine the profitability of using each mulch.

Table 1. results of mulch demonstration

    Please reach out to me at tmorcom@perennia.ca to discuss mulches, our results, or your plans for next year.

    Tim

Tortoise beetles on sweet potatoes

These fascinating beetles are a minor pest of sweet potatoes.  Early in the season, damage can look quite alarming, but rarely hits yield-limiting or economically damaging levels.  The Golden Tortoise Beetle (Charidotella bicolor) and the Mottled Tortoise Beetle (Deloyala guttata) will often come in on slips.  Areas that are protected from predators (i.e. under row cover) tend to show greater damage.  In Nova Scotia, there is typically only one generation per year and they do not overwinter.  Growers typically start noticing feeding damage in early July.  Not to get wildly dorky, but the adults look like if C3PO and R2D2 had a baby (Figure 1).  Adults are 5 – 7 mm in length and are metallic gold or orange, but can shift to a redder colour when disturbed.

Figure 1. Adult tortoise beetles.

You may also notice golden tortoise beetle larvae in your sweet potatoes (Figures 2, 3).  Larvae yellowish to reddish-brown and are broad and flat with spikes.  They have an anal fork and will use it to shovel old skin and fecal matter onto the spines on their back.  This creates a "poop shield", which, unsurprisingly, deters predation.

Figure 2. Tortoise beetle larvae with "poop shield".

Figure 3. Clearly an effective predation deterrent.

Both adults and larvae will feed on sweet potatoes and other members of the Convolvulaceae family, such as field bindweed and morning glory, causing irregular small- to medium-sized holes (Figure 4).  Tortoise beetles are a minor pest of sweet potatoes and chemical control is usually not warranted.  Sweet potatoes are a vigorous crop and will typically outgrow the damage (Figure 5).

Figure 4. Tortoise beetle damage, July 11, 2017.

Figure 5. Tortoise beetle damage in the same field on August 30th, 2017. 

Written in part by Cassidy Coombs, Perennia summer student.

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Wireworms in Nova Scotia

Wireworms in transplants

For those of you who missed Dr. Christine Noronha's presentation on wireworms last week, you can find her presentation here. 

While many areas in Nova Scotia thankfully do not report wireworm problems, there are definitely high populations in some fields.  Last spring, we set traps in a few fields around the province.  Below is a graph from a vegetable field in Colchester County, showing high numbers of Agriotes sputator, one of the more voracious click beetle (adult wireworm) species.  Click beetle flight happens earlier in the warmer parts of the province such as the Valley.

Click beetle catch in Colchester County, 2016.

Perennia has set out some click beetle pheromone traps again this year, and we just collected our first sample.  Below is a photo of our first "haul" from Annapolis County.  On the left is A. obscurus, the middle is A. sputator, and on the right is A. lineatus.  Pheromone traps only attract males, so do not reduce the click beetle/wireworm population, but do give us a good idea of pest levels.  

May 23, 2017 click beetle catch from Annapolis County.

Sweet Potato Production Info Posted

I just finished two fact sheets on sweet potato production:

Commerical Sweet Potato Production
Small Scale Sweet Potato Production

They are also listed under 'Sweet Potato' on our vegetable crop page.

If you have any questions, please let me know.

Viliam